CN102024950A - Positive electrode active material, positive electrode, nonaqueous electrolyte cell, and method of preparing positive electrode active material - Google Patents

Abstract

The invention provides a positive electrode active material, a preparation method thereof, a positive electrode and a nonaqueous electrolyte battery. The positive electrode active material is prepared by mixing a lithium-containing compound, a compound containing a transition metal to be contained in a solid solution, and a compound containing a metal element M2 other than a transition metal, and firing the mixture to form a composite oxide depositing a compound containing at least one element selected from sulfur, phosphorus, and fluorine on the surface of the composite oxide particle; and firing a compound containing at least one element selected from sulfur, phosphorus, and fluorine deposited thereon Composite oxide particles of the compound; thus each composite oxide particle has such a concentration gradient that the concentration of the metal element M2 increases from the center of the composite oxide particle toward the surface, and the metal element M2 is selected from the group consisting of sulfur, phosphorus, and fluorine At least one element of is present in the form of being aggregated on the surface of the composite oxide particles.

Description

Positive electrode active material and preparation method thereof, positive electrode and non-aqueous electrolyte battery

References to related applications

This application contains Japanese Prior Patent Applications JP 2009-208505, 2010-105024 filed with the Japan Patent Office on September 9, 2009, April 30, 2010, November 18, 2009 and April 30, 2010, respectively , 2009-263301 and 2010-105025, the entire contents of which are incorporated herein by reference. the

technical field

The invention relates to a positive pole active material, a positive pole, a nonaqueous electrolyte battery and a method for preparing the positive pole active material. More particularly, the present invention relates to a positive electrode active material, a positive electrode, a nonaqueous electrolyte battery and a preparation thereof by which a nonaqueous electrolyte battery having high performance and exhibiting little capacity degradation can be realized when charging and discharging are performed in a high temperature environment Method of positive active material. Specifically, the present invention relates to a positive electrode active material including a lithium-transition metal composite oxide. the

Background technique

In recent years, with the spread of portable devices such as video cameras and notebook-type personal computers, the demand for small and high-capacity secondary cells and batteries has been increasing. Secondary batteries currently in use include nickel-cadmium batteries and nickel-hydrogen batteries using alkaline electrolytes. However, these secondary batteries have disadvantages in that the battery voltage is as low as about 1.2 V and it is difficult to increase the energy density. Therefore, lithium-ion secondary batteries with higher voltage than other battery systems and higher energy density are widely used today. the

However, due to the high charging voltage compared with other battery systems, lithium ion secondary batteries have a problem in that their capacity is deteriorated and their usefulness is lifespan will be shortened. Furthermore, when a lithium ion secondary battery is used under high-temperature environmental conditions, an increase in internal resistance occurs, making it very difficult to secure a sufficient capacity. There is a strong need for solutions to these problems. the

LiCoO ₂ , LiNiO ₂ and other lithium-transition metal composite oxide particles are widely used as positive electrode active materials for lithium ion secondary batteries. Recently, various techniques have been proposed to improve the state of the particle surface by forming a coating layer on the particle surface or diffusing some material from the particle surface to obtain better performance of lithium-transition metal composite oxide particles.

For example, in Japanese Patent No. 3197763 (hereinafter, referred to as Patent Document 1), a method of adding a metal salt or hydroxide to a positive electrode is shown. Furthermore, Japanese Patent Laid-Open No. Hei 5-47383 (hereinafter, referred to as Patent Document 2) shows a technique of coating the surface of lithium cobalt oxide (LiCoO ₂ ) with phosphorus (P). Japanese Patent No. 3172388 (hereinafter referred to as Patent Document 3) and Japanese Patent No. 3691279 (hereinafter referred to as Patent Document 4) show a method of coating the surface of a positive electrode active material or a positive electrode with a metal oxide. method.

Japanese Patent Publication No. Hei 7-235292 (hereinafter referred to as Patent Document 5), Japanese Patent Publication No. 2000-149950 (hereinafter referred to as Patent Document 6), Japanese Patent Publication No. 2000-156227 (hereinafter referred to as Patent Document 6) , referred to as Patent Document 7), Japanese Patent Laid-Open No. 2000-164214 (hereinafter referred to as Patent Document 8), Japanese Patent Laid-Open No. 2000-195517 (hereinafter referred to as Patent Document 9), Japanese Patent Laid-Open No. No. 2001-196063 (hereinafter, referred to as Patent Document 10), Japanese Patent Laid-Open No. 2002-231227 (hereinafter, referred to as Patent Document 11) and the like show that in which a lithium-transition metal composite oxide is uniformly coated A method of coating the surface of a particle and a method in which a complex oxide is diffused from the surface of a particle. Furthermore, Japanese Patent Laid-Open No. 2001-256979 (hereinafter, referred to as Patent Document 12) shows a cathode active material in which lumps of metal oxide are deposited on a metal oxide layer. Japanese Patent Laid-Open No. 2002-164053 (hereinafter, referred to as Patent Document 13) shows a positive electrode active material in which at least one surface treatment layer containing at least two coating elements is formed on the surface of a core containing a lithium compound . the

Japanese Patent Publication No. 3157413 (hereinafter, referred to as Patent Document 14) discloses a positive electrode active material in which a coating including a metal fluoride is provided on the surface of particles, and Japanese Patent Publication No. 3141858 (hereinafter, Called Patent Document 15) shows a coating comprising a crystalline metal fluoride. Furthermore, Japanese Patent Laid-Open No. 2003-221235 describes specifying the XPS (X-ray Photoelectron Spectroscopy) energy of fluorine on the surface of particles. When the inventors of the present invention prepared a positive electrode active material by mixing metal fluorides and heat-treating the mixture according to the disclosure, a practical effect on high-temperature storage stability was observed, but the effect was limited to the effect on the surface of the particles and based on actual Use performance is not sufficient. Also, U.S. Patent No. 7,364,793 (hereinafter, referred to as Patent Document 16) discloses a material obtained by a method in which a compound having a high affinity for lithium and capable of donating cations is reacted with a lithium-transition metal composite oxide . the

Contents of the invention

However, according to adding a metal salt or hydroxide to a lithium-transition metal oxide having a general uniform form as in the method of Patent Document 1, the resistance of the electrode increases and it is difficult to obtain a sufficient capacity. In the method of Patent Document 2, the capacity decrease due to the coating is large, making the positive electrode active material unsatisfactory for practical use. If only the coating elements, coating methods, and coating forms disclosed in Documents 3 and 4 are utilized, the methods of Patent Documents 3 and 4 are all unconvincing as techniques for improving battery performance under high-temperature conditions. satisfied. In addition, it was also found that increasing the coating amount so as to obtain a sufficient effect results in hindering the diffusion of lithium ions, making it very difficult to obtain a sufficient capacity at a charge-discharge current value in the practical application field. Therefore, this method was found to be unsatisfactory. the

The methods disclosed in Patent Documents 4 to 9 were found to be unsatisfactory for improving cycle characteristics to a high degree and suppressing resistance increase during high-temperature use, although high capacity can be maintained by this method. When a positive electrode active material is prepared by the method and structure disclosed in Patent Document 12, it is difficult to obtain sufficient charge-discharge efficiency, and the capacity is largely lowered. In the method of Patent Document 13, if the surface treatment is used alone, the effect due to this method is limited. In addition, when the positive electrode active material was actually prepared by the method disclosed in this document, a uniform multilayer was formed, and the effect of preventing an increase in resistance was not found especially when used at a high temperature. the

Regarding the method according to Patent Document 15, simple coating with a metal fluoride having low electron conductivity and lithium ion conductivity leads to a significant decrease in charge-discharge performance, and its effect on charge-discharge characteristics in a high-temperature environment is insufficient . When the inventors of the present invention prepared a positive electrode active material by the method disclosed in Patent Document 16, unevenness or exfoliation of materials added as coating materials occurred, and inactive compounds such as oxides and lithium fluoride were generated, so that The coating function is not fully represented. In addition, it is difficult to obtain charge-discharge performance at a practical use level because the migration of lithium ions is hindered at the solid-liquid interface at the time of charge-discharge. In addition, a tendency of capacity reduction was also observed due to loss of lithium from the lithium-transition metal composite oxide. Therefore, the material according to this document is unsatisfactory. the

Therefore, there is a need for a positive electrode active material that has a high capacity, is excellent in charge-discharge cycle characteristics, and exhibits little deterioration when being used in a high-temperature environment, a positive electrode and a nonaqueous electrolyte secondary battery using such a positive electrode active material, and the preparation of such a positive electrode active material. Method of positive active material. the

According to an embodiment of the present invention, there is provided a positive electrode active material prepared by mixing a lithium-containing compound, a compound containing a transition metal to be contained in a solid solution, and a compound containing a metal element M2 other than a transition metal , and firing the mixture to form composite oxide particles; depositing a compound containing at least one element selected from sulfur (S), phosphorus (P) and fluorine (F) on the surface of the composite oxide particles; and firing Composite oxide particles having deposited thereon a compound containing at least one element selected from sulfur (S), phosphorus (P) and fluorine (F); thus each composite oxide particle has such a concentration gradient: The concentration of the metal element M2 increases from the center of the composite oxide particle to the surface, and at least one element selected from sulfur (S), phosphorus (P) and fluorine (F) is aggregated in the composite form on the surface of oxide particles. the

According to another embodiment of the present invention, there is provided a positive electrode comprising a positive electrode active material prepared by: combining a lithium-containing compound, a compound containing a transition metal to be contained in a solid solution, and containing a metal other than a transition metal Compounds of the element M2 are mixed, and the mixture is fired to form composite oxide particles; depositing on the surface of the composite oxide particles contains at least one element selected from the group consisting of sulfur (S), phosphorus (P) and fluorine (F). compound; and firing composite oxide particles on which a compound containing at least one element selected from sulfur (S), phosphorus (P) and fluorine (F) is deposited; thus each composite oxide particle has Such a concentration gradient: the concentration of the metal element M2 increases from the center of the composite oxide particle to the surface, and at least one element selected from sulfur (S), phosphorus (P) and fluorine (F) is gathered in the composite form on the surface of oxide particles. the

According to another embodiment of the present invention, there is provided a non-aqueous electrolyte battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode includes a positive electrode active material prepared by the following steps: mixing a lithium-containing compound containing a transition Compounds of metals, and compounds containing metal elements M2 different from transition metals, and firing the mixture to form composite oxide particles; ) and a compound of at least one element of fluorine (F); and a composite oxidation of firing a compound containing at least one element selected from sulfur (S), phosphorus (P) and fluorine (F) deposited thereon material particles; thus each composite oxide particle has such a concentration gradient that the concentration of the metal element M2 increases from the center of the composite oxide particle to the surface, and the metal element M2 is selected from the group consisting of sulfur (S), phosphorus (P) and fluorine ( At least one element in F) exists in the form of being aggregated on the surface of the composite oxide particles. the

Pyrolysis of the compound containing at least one element selected from the group consisting of sulfur (S), phosphorus (P) and fluorine (F) of the positive electrode active material of the positive electrode and non-aqueous electrolyte battery of the present invention, or the compound of the positive electrode active material The (ie, thermal decomposition) product preferably has a melting point of 70° C. or more and 600° C. or less, and also preferably has an average diameter of 30 μm or less. the

According to yet another embodiment, there is provided a method for preparing a positive electrode active material, comprising the steps of: mixing a lithium-containing compound, a compound containing a transition metal to be contained in a solid solution, and a compound containing a metal element M2 other than a transition metal , and firing the mixture to form composite oxide particles; depositing a compound containing at least one element selected from sulfur (S), phosphorus (P) and fluorine (F) on the surface of the composite oxide particles; and firing Composite oxide particles having deposited thereon a compound containing at least one element selected from sulfur (S), phosphorus (P) and fluorine (F); thus each composite oxide particle has such a concentration gradient: The concentration of the metal element M2 increases from the center of the composite oxide particle toward the surface, and at least one element selected from the group consisting of sulfur (S), phosphorus (P), and fluorine (F) is allowed to accumulate on the surface of the composite oxide particle form exists. the

The compound containing at least one element selected from the group consisting of sulfur (S), phosphorus (P) and fluorine (F) deposited on the surface of the composite oxide particles is preferably melted or thermally decomposed to be uniformly present in the composite oxide particles. on the surface of the particles. Also preferably on the surface of the composite oxide particle, the cation of the compound containing at least one element selected from the group consisting of sulfur (S), phosphorus (P) and fluorine (F) deposited on the surface of the composite oxide particle is removed, And the anion of the compound is reacted with the element contained in the composite oxide particle. the

In addition, according to another embodiment of the present invention, there is provided a positive electrode active material including lithium-transition metal composite oxide particles containing lithium, a main transition metal M1, and a metal different from the main transition metal. The metal element M2 of the metal M1, the metal element M2 has a concentration gradient of the metal element M2 from the center of each particle to the surface, wherein the ratio d (%) satisfies 0.020≤d≤0.050 from the surface to a certain depth, molar The fraction r (%) satisfies the formula 0.20≤r≤0.80, wherein the ratio d (%)=[(mass of the main transition metal M1)+(mass of the metal element M2)]/(mass of the whole particle), and wherein the mole fraction r=(substance amount of metal element M2)/[(substance amount of main transition metal M1)+(substance amount of metal element M2)]. the

According to still another embodiment of the present invention, there is provided a positive electrode comprising a positive electrode active material comprising lithium-transition metal composite oxide particles comprising lithium, a main transition metal M1 and different In the metal element M2 of the main transition metal M1, the metal element M2 has a concentration gradient of the metal element M2 from the center of each particle to the surface, wherein the ratio d (%) from the surface to a certain depth satisfies 0.020≤d≤0.050 Within the scope, mole fraction r (%) satisfies the formula 0.20≤r≤0.80, wherein ratio d (%)=[(mass of main transition metal M 1)+(mass of metal element M2)]/(mass of whole particle) , and wherein the mole fraction r=(the amount of matter of the metal element M2)/[(the amount of matter of the main transition metal M1)+(the amount of matter of the metal element M2)]. the

According to another embodiment of the present invention, there is provided a non-aqueous electrolyte battery including a positive electrode, a negative electrode, and an electrolyte, the positive electrode includes a positive electrode active material comprising lithium-transition metal composite oxide particles, and the lithium-transition metal composite oxide particles Containing lithium, a main transition metal M1, and a metal element M2 different from the main transition metal M1, the metal element M2 has a concentration gradient of the metal element M2 from the center of each particle to the surface, wherein the ratio d( %) satisfies the range of 0.020≤d≤0.050, and the mole fraction r (%) satisfies the formula 0.20≤r≤0.80, wherein the ratio d (%)=[(mass of main transition metal M1)+(mass of metal element M2) ]/(the mass of the whole particle), and wherein the mole fraction r=(the amount of matter of the metal element M2)/[(the amount of matter of the main transition metal M1)+(the amount of matter of the metal element M2)]. the

According to the present invention, by controlling the mole fraction r (%) to satisfy the formula 0.20 ≤ r ≤ 0.80 in the range of satisfying 0.020 ≤ d ≤ 0.050 from the surface to a certain depth ratio d (%) to suppress positive electrode active material-electrolyte boundary Reaction. the

In the present invention, each composite oxide particle has a concentration gradient such that the concentration of the metal element M2 increases from the center to the surface of the composite oxide particle, and is selected from sulfur (S), phosphorus (P), and fluorine (F) At least one element of is present on the surface of the composite oxide particle in the form of being aggregated on the surface of the composite oxide particle. Therefore, the stability of the positive electrode active material and the stability at the interface can be ensured. the

According to the present invention, a battery that has a high capacity, is excellent in charge-discharge cycle characteristics, and exhibits little deterioration when used in a high-temperature environment can be realized. the

Description of drawings

1 is a perspective view showing a configuration example of a nonaqueous electrolyte battery according to an embodiment of the present invention;

Fig. 2 is a sectional view along the line II-II of Fig. 1 of the wound electrode body shown in Fig. 1;

3 is a cross-sectional view showing a configuration example of a non-aqueous electrolyte battery according to an embodiment of the present invention;

Figure 4 is a cross-sectional view showing a portion of the wound electrode body shown in Figure 3 in enlarged form; and

5 is a cross-sectional view showing a configuration example of a non-aqueous electrolyte battery according to an embodiment of the present invention. the

Detailed ways

Now, embodiments of the present invention will be described below with reference to the accompanying drawings. The embodiments described below are specific examples of the present invention, and at the same time, various limitations considered to be technically preferable are provided. However, the scope of the present invention is not limited by these embodiments unless a description is given in the following description indicating a specific limitation to the present invention. In addition, description will be made in the following order. the

1. First embodiment (first example of non-aqueous electrolyte battery)

2. The second embodiment (second example of non-aqueous electrolyte battery)

3. The third embodiment (the third example of the non-aqueous electrolyte battery)

4. Fourth embodiment (fourth example of non-aqueous electrolyte battery)

5. Fifth embodiment (fifth example of non-aqueous electrolyte battery)

6. Other implementation methods

[Summary of the present invention]

Lithium-containing transition metal oxides such as lithium cobaltate (LiCoO ₂ ) and lithium nickelate (LiNiO ₂ ) are widely used as positive electrode active materials in lithium ion secondary batteries. However, they suffer from stability problems in their state of charge. In particular, transition metal components may be eluted from the positive electrode due to increased reactivity at the interface between the positive electrode active material and the electrolyte, resulting in degradation of the active material or precipitation of the eluted metal on the negative electrode side. As a result, occlusion (intercalation) and release (deintercalation) of lithium (Li) are hindered.

In addition, such a positive electrode active material as mentioned above is considered to accelerate the decomposition reaction of the electrolyte at the interface, resulting in the formation of a coating on the electrode surface or generation of gas, which leads to deterioration of battery characteristics. At the same time, under the condition of properly designing the positive electrode-negative electrode ratio, the energy density of the battery during charging can be improved by charging in a manner that reaches a maximum charging voltage of at least 4.20V (preferably at least 4.35V, more preferably at least 4.40V). However, it has become clear that in the case where the charging voltage is increased and charge-discharge cycles are repeated under high charge-voltage conditions of 4.25 V or higher, the above-mentioned deterioration of the active material or electrolyte is accelerated, resulting in reduced charge-discharge cycle life or high temperature Performance degradation after saving. the

Therefore, the inventors of the present invention conducted extensive and intensive studies. After research, they found that in the case of using a lithium-containing metal composite oxide having an improved particle surface, the presence of a metal compound on the particle surface produces a highly synergistic or novel effect on the improvement of battery characteristics. The present invention based on this finding aims to provide a positive electrode active material for a lithium ion secondary battery that greatly improves the characteristics and stability of the battery. the

1. First embodiment (first example of non-aqueous electrolyte battery)

FIG. 1 is a perspective view showing a configuration example of a nonaqueous electrolyte battery according to a first embodiment of the present invention. The nonaqueous electrolyte battery is, for example, a nonaqueous electrolyte secondary battery. This nonaqueous electrolyte battery having a flat overall shape has a configuration in which a wound electrode body 10 mounted with a positive electrode lead 11 and a negative electrode lead 12 is housed in a film-like package (casing member) 1 . the

Both the positive electrode lead 11 and the negative electrode lead 12 are shaped like a rectangular plate, for example, and they are drawn out in the same direction from the inside of the package 1 toward the outside, for example. For example, the cathode lead 11 is made of a metal material such as aluminum (Al), and the anode lead 12 is made of a metal material such as nickel (Ni), for example. the

The packages 1 are each constituted by, for example, a laminated film having a structure in which an insulating layer, a metal layer, and an outermost layer are stacked in this order and adhered to each other by lamination or the like. For example, the package 1 is configured such that the insulating layer side is disposed on the inside, and each outer edge portion is fixed to each other by melting or by using an adhesive. the

The insulating layer is composed of, for example, polyolefin resins such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, and copolymers thereof. Such polyolefin resins ensure low water permeability and are excellent in airtightness. The metal layer is formed of a foil-like or plate-like member of aluminum, stainless steel, nickel, iron, or the like. The outermost layer may be made of, for example, a resin similar to the insulating layer, or made of nylon or the like. Such material guarantees high strength against cracking or puncturing. The package 1 may also have other layers than the above-mentioned insulating layer, metal layer and outermost layer.

Between the package 1 and each of the positive electrode lead 11 and the negative electrode lead 12, an adhesive film 2 is inserted for improving the adhesion of each of the positive electrode lead 11 and the negative electrode lead 12 to the inside of the package 1 and for Prevent the penetration of outside air. Adhesive film 2 is formed of a material having adhesive (fixed contact) properties to each of cathode lead 11 and anode lead 12 . In the case where the positive electrode lead 11 and the negative electrode lead 12 are composed of the above-mentioned metal material, the adhesive film 2 is preferably formed of, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, or the like. the

FIG. 2 is a cross-sectional view of the wound electrode body 10 shown in FIG. 1 along line II-II in FIG. 1 . The wound electrode body 10 has a structure in which a positive electrode 13 and a negative electrode 14 are stacked together with a separator 15 and an electrolyte 16 in between, and the outermost peripheral portion thereof is protected by a protective tape 17 . the

[Positive pole]

The positive electrode 13 has, for example, a positive electrode current collector 13A and positive electrode active material layers 13B respectively provided on both sides of the positive electrode current collector 13A. The positive electrode active material layer may be provided only on one side of the positive electrode current collector 13A. As positive electrode current collector 13A, for example, metal foil such as aluminum foil can be used. the

The positive electrode active material layer 13B includes, as a positive electrode active material, one or two or more positive electrode materials capable of occluding and releasing electrode reactants. The positive electrode active material layer 13B further includes a conductive aid such as a carbon material and a binder such as polyvinylidene fluoride or polytetrafluoroethylene. the

[Positive electrode active material]

The positive electrode active material is, for example, composite oxide particles containing therein a metal element M2 different from the main transition metal M1 and having a concentration gradient of the metal element M2 from the center to the surface of each particle. The concentration gradient means that the concentration of the metal element M2 increases as it approaches the particle surface. The composite oxide particle is a lithium-containing transition metal composite oxide in which at least one element X selected from sulfur (S), phosphorus (P), and fluorine (F) exists in an aggregated form on the surface of the composite oxide particle particle. Incidentally, the state of the surface of the lithium-transition metal composite oxide can be confirmed by observing the obtained powder under SEM/EDX (scanning electron microscope/energy dispersive X-ray spectrometer). the

Metal element M2 is not particularly limited. However, it is preferable that the composite oxide particle is a particle of a lithium-containing transition metal composite oxide prepared by a method in which the metal element M2 is pre-existed inside the composite oxide particle, and the metal element M2 is made to contain sulfur (S ), phosphorus (P) and fluorine (F) react with a compound of at least one element X to increase the concentration of the metal element M2 at the particle surface. the

Therefore, the metal element M2 is uniformly distributed inside the composite oxide particles in advance, and then the concentration of the metal element M2 on the particle surface is increased, whereby the metal element M2 can be uniformly present on the particle surface. As a result, the modifying effect of the metal element M2 on the particle surface can be maximally exhibited. the

The metal element M2 is preferably, on a solid solution basis, at least one element that can replace the main transition metal element M1 in the interior of the composite oxide particle. More preferably, the metal element M2 is selected from the group consisting of manganese (Mn), magnesium (Mg), aluminum (Al), nickel (Ni), boron (B), titanium (Ti), cobalt (Co) and iron (Fe) At least one element in the group of . It is effective for the metal element M2 to exist on the particle surface in a state of substituting the main transition metal element A or in a state of diffusing to the inside near the particle surface so as to exhibit a continuous concentration gradient toward the center of each particle. the

Incidentally, the concentration of magnesium can be confirmed by cutting a section of the lithium-transition metal composite oxide and measuring the distribution in the radial direction by Auger electron spectroscopy. the

In addition, the reaction of the metal element M2 for increasing the concentration of the metal element M2 on the surface of the particles with a compound containing at least one element selected from sulfur (S), phosphorus (P) and fluorine (F) is preferably carried out in lithium (Li ) in the presence of compounds. In the case where the reaction is performed in the coexistence of a Li compound, it is possible to adjust the amount of Li in the lithium-containing composite oxide and suppress a decrease in capacity due to surface modification. the

As the lithium-transition metal composite oxide inside the particles, one of various known substances can be used. However, preferably, the lithium-transition metal composite oxide has a layered rock salt structure and the main transition metal element A constituting it is selected from nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe) at least one of the substances. Such a substance guarantees a high capacity. Furthermore, known substances based on solid solutions into which small amounts of additional elements have been introduced as substitutes can also be used. the

Incidentally, the composite oxide particles used as the base material for the positive electrode are, for example, lithium composite oxide particles having a layered rock salt structure and an average composition represented by the following chemical formula (chemical formula 1). the

(chemical formula 1)

Li _a A _b M _1-b O _c

In this formula, M is preferably selected from manganese (Mn), magnesium (Mg), aluminum (Al), nickel (Ni), boron (B), titanium (Ti), cobalt (Co) and iron (Fe). at least one element of ; a, b, and c are numbers in the range of 0.2≤a≤1.4, 0≤b≤1.0, and 1.8≤c≤2.2; in addition, the constituent ratio of lithium varies with the charging/discharging state, The value of a shown here represents a value in a fully discharged state. the

In the chemical formula (chemical formula 1), the range of the value of a is, for example, 0.2≦a≦1.4. If the value of a is too small, the layered rock-salt structure, which is the basic crystal structure of the lithium composite oxide, is broken, thereby making repeated charging difficult and the capacity significantly lowered. On the other hand, if the value of a is too large, lithium diffuses to the outside of the composite oxide particles, hinders the control of alkalinity in subsequent processing steps, and finally causes a problem of promoting gelation during the kneading of the positive electrode slurry . the

Incidentally, the lithium composite oxide in the above formula (Chemical Formula 1) is set so as to have a lithium content exceeding the related art. Specifically, the value of a representing the ratio of lithium in the lithium composite oxide in the above formula (Chemical Formula 1) may be greater than 1.2. Here, the value of 1.2 has been disclosed in the related art as the constituent ratio of lithium in this type of lithium composite oxide, and since it has the same crystal structure as in the case of a=1, the same Work effect (refer to, for example, the applicant's prior application: Japanese Patent Laid-Open No. 2008-251434). the

Even when the value of a representing the constituent ratio of lithium in the lithium composite oxide of the above formula (Chemical Formula 1) is greater than 1.2, the crystal structure of the lithium composite oxide is the same as when the value of a is not greater than 1.2. In addition, even when the value of a representing the constituent ratio of lithium in the above formula (Chemical Formula 1) is greater than 1.2, if the value is not greater than 1.4, the transition of lithium composite oxide is formed in the oxidation-reduction reaction accompanying the charge-discharge cycle. The chemical state of the metal is not much different from the case where the value of a is not greater than 1.2. the

The value range of b is, for example, 0≤b≤1.0. If the value of b decreases below this range, the discharge capacity of the positive electrode active material decreases. On the other hand, if the value of b is increased above this value, the stability of the crystal structure of the composite oxide particles decreases, resulting in decreased charge-discharge retention capacity and decreased safety of the positive electrode active material. the

The value range of c is, for example, 1.8≦c≦2.2. In the case where the value of c is lower than the range and in the case where the value is higher than the range, the stability of the crystal structure of the composite oxide particles will decrease, resulting in a decrease in the charge-discharge retention capacity of the positive electrode active material and a decrease in safety. decrease, and lead to a decrease in the discharge capacity of the positive electrode active material. the

[Particle diameter]

The positive active material preferably has an average particle diameter of 2.0 μm to 50 μm. If the average particle diameter is less than 2.0 μm, peeling of the positive electrode active material layer may occur when the positive electrode active material layer is pressed in the process of manufacturing the positive electrode. In addition, due to the increased surface area of the positive active material, it is necessary to increase the addition amount of the conductive aid and the binder, so that the energy density per unit weight tends to be lowered. On the other hand, if the average particle diameter exceeds 50 μm, the particles tend to pierce the separator, causing a short circuit. the

The positive electrode 13 preferred above has a thickness of not more than 250 μm. the

[negative pole]

The negative electrode 14 has, for example, a negative electrode current collector 14A and negative electrode active material layers 14B respectively provided on both sides of the negative electrode current collector 14A. The anode active material layer 14B may be provided on only one side of the anode current collector 14A. The anode current collector 14A is composed of, for example, metal foil such as copper foil. the

For example, the anode active material layer 14B is configured to contain at least one anode material capable of occluding and releasing lithium as an anode active material, and may contain a conductive aid and/or a binder if necessary. the

Examples of negative electrode materials capable of occluding and releasing lithium include carbon materials such as graphite, hardly graphitizable carbon, or easily graphitizable carbon, which may be used alone or as a mixture of two or more thereof. In addition, two or more such materials different in average particle diameter may be used as a mixture. the

Other examples of negative electrode materials capable of occluding and releasing lithium include those containing, as constituent elements, metal or semimetal elements capable of forming an alloy with lithium. Specific examples of such materials include simple substances, alloys and compounds of metal elements capable of forming alloys with lithium and simple substances, alloys and compounds of semimetal elements capable of forming alloys with lithium, and elements having these simple substances, alloys and compounds in at least part thereof. A material of more than one phase in a compound. the

Examples of such metal or semimetal elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), cadmium (Cd ), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) and hafnium (Hf), among which preferred is a metal or semimetal element of Group 14 in the long period type periodic table, and silicon (Si) and tin (Sn) are particularly preferable. Silicon (Si) and tin (Sn) have a high ability to occlude and release lithium, thus ensuring high energy density. the

Examples of alloys of silicon (Si) include those comprising tin (Sn), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium ( At least one of the group consisting of In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb) and chromium (Cr) as the second silicon (Si) An alloy of constituent elements. Examples of alloys of tin (Sn) include those containing silicon (Si), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium ( At least one of the group consisting of In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb) and chromium (Cr) as the second An alloy of constituent elements.

Examples of compounds of silicon (Si) or tin (Sn) include those containing oxygen (O) or carbon (C), and the compound may contain the above-mentioned second constituent element other than silicon (Si) or tin (Sn) one or more of. the

[diaphragm]

The separator 15 may be formed by using any material that is electrically stable, chemically stable with respect to the cathode active material, the anode active material, and the solvent, and non-conductive. Examples of materials that can be used here include polymer nonwoven fabrics, porous films, and paper-like sheets of glass or ceramic fibers, which can be used in the form of a multilayer laminate. Particularly preferred is a porous polyolefin membrane, which can be used in the form of a composite with a heat-resistant material formed of polyimide, glass, or ceramic fibers or the like. the

[Electrolyte]

The electrolyte 16 includes an electrolytic solution and a holder that can hold the electrolytic solution, the holder includes a polymer compound, and is in a so-called gelled state. The electrolytic solution contains electrolyte salts and solvents that can be used to dissolve the electrolyte salts. Examples of the electrolyte salt include lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ and LiAsF ₆ , which may be used alone or in combination of two of them. Use a mixture of the above.

Examples of the solvent include lactones such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, etc., such as ethylene carbonate, propylene carbonate, butylene carbonate, ethylene carbonate, Carbonate solvents such as vinyl ester, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, etc., such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1 , ether solvents such as 2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, etc., nonaqueous solvents such as nitrile solvents such as acetonitrile, nonaqueous solvents such as sulfolane solvents, phosphoric acids, phosphate ester solvents, and pyrrolidone. These solvents may be used alone or as a mixture of two or more of them. the

Furthermore, the solvent preferably contains a compound having a structure in which hydrogen atoms of a cyclic ester or a linear ester are partially or completely fluorinated (substituted by a fluorine atom). Preferred as fluorinated compound is difluoroethylene carbonate (4,5-difluoro-1,3-dioxolan-2-one). Thereby, even in the case of using the negative electrode 14 including a compound including silicon (Si), tin (Sn), germanium (Ge) or the like as the negative electrode active material, charge-discharge cycle characteristics can be improved. In particular, difluoroethylene carbonate has an excellent improvement effect on cycle characteristics. the

The high-molecular compound may be any high-molecular compound that is gelled by absorbing a solvent. Examples of high molecular compounds include fluorinated high molecular compounds such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, etc., ether high molecular compounds such as polyethylene oxide, cross-linked polymers containing polyethylene oxide etc., and polymer compounds containing polyacrylonitrile, polypropylene oxide or polymethyl methacrylate as repeating units. These polymer compounds can be used alone or in mixture of two or more of them. the

In particular, from the viewpoint of oxidation-reduction stability, fluorinated high molecular compounds are desirable, among which copolymers containing vinylidene fluoride and hexafluoropropylene as components are preferable. Furthermore, the copolymer may contain monoesters of unsaturated dibasic acids such as monomethyl maleate, etc., vinyl halides such as trifluoroethylene, etc., cyclic carbonates of unsaturated compounds such as vinylene carbonate, or epoxy group-containing A group of acryloyl vinyl monomers are used as components, which makes it possible to obtain higher characteristics. the

In addition, as the solid electrolyte, an inorganic solid electrolyte and a polymer solid electrolyte can be used as long as the solid electrolyte has lithium ion conductivity. Examples of inorganic solid electrolytes include lithium nitride and lithium iodide. All polymer solid electrolytes include electrolyte salts and polymer compounds that can be used to dissolve the electrolyte salts. Examples of the polymer compound include ether polymers such as poly(ethylene oxide), its cross-linked products, etc., poly(methacrylate) polymers, acrylate polymers, etc., which may be used alone or as one of them. Two or more copolymers, or a mixture of two or more of them are used. the

[Method of manufacturing positive electrode]

First, composite oxide particles containing the metal element M1 in the present invention were synthesized. The method for synthesizing composite oxide particles is not particularly limited. Furthermore, as a compound for reacting the composite oxide particles with a compound containing at least one element selected from sulfur (S), phosphorus (P) and fluorine (F) so that the concentration of the metal element M2 on the surface of the particles increases As a method, various known methods can be used. the

In addition, methods for coating the surface of composite oxide particles include methods in which lithium-transition metal composite oxides containing metal element M2 and containing metal elements selected from sulfur ( A compound of at least one element of S), phosphorus (P) and fluorine (F) is pulverized, mixed and coated (deposited). In carrying out this operation, it is effective to add a certain amount of a liquid component, which may be, for example, water. In addition, coating (deposition) by mechanochemical treatment or coating (deposition) with a metal compound by a vapor phase method such as sputtering, CVD (Chemical Vapor Deposition) or the like may also be employed. the

Also, by mixing raw materials in water or in a solvent such as ethanol, by crystallization via neutralization in a liquid phase, or by other similar methods can be formed on the lithium-transition metal composite oxide containing selected from sulfur (S) , the surface of at least one element of phosphorus (P) and fluorine (F). After allowing at least one element selected from sulfur (S), phosphorus (P), and fluorine (F) to thereby exist on the lithium-transition metal composite oxide containing the metal element M2, heat treatment is preferably performed so that the metal element M2 Concentration increases at the particle surface. For example, heat treatment may be performed at 350°C to 900°C. The obtained lithium-transition metal composite oxide may be a composite oxide that has been treated by a known technique for controlling powder properties. the

Subsequently, a positive electrode active material, a binder, and a conductive aid such as a carbon material are mixed together to prepare a positive electrode composition. The cathode composition is dispersed in a solvent such as N-methyl-2-pyrrolidone to prepare a cathode composition slurry. The binder can be polyvinylidene fluoride, polytetrafluoroethylene, etc. the

Next, the cathode composition slurry was applied to the cathode current collector 13A, and dried. After that, compression molding is performed using a roll pressing machine or the like to form the positive electrode active material layer 13B, whereby the positive electrode 13 is obtained. Incidentally, if necessary, a conductive aid such as a carbon material is mixed at the time of preparing the positive electrode composition. the

[Method of manufacturing negative electrode]

Next, the negative electrode 14 was manufactured in the following manner. First, a negative electrode active material and a binder are mixed with each other to prepare a negative electrode composition, and the negative electrode composition is dispersed in a solvent such as N-methyl-2-pyrrolidone to prepare a negative electrode composition slurry. Subsequently, the negative electrode composition slurry was applied to the negative electrode collector 14A, and the solvent was evaporated. After that, compression molding is performed using a roll press machine or the like to form the negative electrode active material layer 14B, whereby the negative electrode 14 is obtained. the

[Method for producing non-aqueous electrolyte battery]

For example, a nonaqueous electrolyte battery can be produced in the following manner. First, a precursor solution including an electrolytic solution, a polymer compound, and a mixed solvent is applied to each of the positive electrode 13 and the negative electrode 14 , and the mixed solvent is evaporated to form the electrode 16 . After that, the positive electrode lead 11 was connected to the end of the positive electrode current collector 13A by welding, and the negative electrode lead 12 was connected to the end of the negative electrode current collector 14A by welding. the

Next, the positive electrode 13 and the negative electrode 14 in which the electrolyte 16 is formed are stacked together with the separator 15 in between to form a stacked body, the stacked body is wound in the longitudinal direction, and the protective tape 17 is adhered to the uppermost end of the wound body. outer peripheral portion to form the wound electrode body 10 . Finally, for example, wound electrode body 10 is sandwiched between packages 1 , and outer peripheral portions of packages 1 are adhered to each other by thermal fusion or the like to seal rolled electrode body 10 in package 1 . In this case, the adhesive film 2 is inserted between each of the cathode lead 11 and the anode lead 12 and each of the package 1 . In this way, the nonaqueous electrolyte battery as shown in FIGS. 1 and 2 was completed. the

In addition, a nonaqueous electrolyte battery can also be produced in the following manner. First, the positive electrode 13 and the negative electrode 14 are fabricated in the above-described manner, and the positive electrode lead 11 and the negative electrode lead 12 are adhered to the positive electrode 11 and the negative electrode 12 , respectively. Then, the positive electrode 13 and the negative electrode 14 are stacked together with the separator 15 in between to form a stacked body, the stacked body is wound, and the protective tape 17 is adhered to the outermost peripheral portion of the wound body to form a wound electrode A jellyroll of the precursor of the body 10 . Next, this jelly roll is sandwiched between packages 1, and the outer peripheral edge portion except for one side of the pack 1 is thermally fused to obtain a pouch-like shape, thereby housing the jelly roll in the pack 1 . Subsequently, an electrolyte composition containing an electrolytic solution, a monomer as a raw material for a polymer compound, a polymerization initiator, and if necessary, other materials such as a polymerization inhibitor is prepared, and the electrolyte composition is introduced into the package 1 . the

After introducing the electrolyte composition, the opening portion of the package 1 is sealed by thermal fusion under a vacuum atmosphere. Next, heat will be applied to polymerize a monomer or monomers to form a polymer compound, thereby forming the gel electrolyte 16, and the nonaqueous electrolyte battery as shown in FIGS. 1 and 2 is assembled. the

Details of the improvement in cycle characteristics and the like are still unclear, but it is considered that the improvement is achieved by the following mechanism. In a charged lithium-ion secondary battery, the positive electrode is in a strongly oxidized state, and the electrolyte solution in contact with the positive electrode is in an environment where oxidation and decomposition are prone to occur, especially in a high-temperature environment. When the electrolyte solution is decomposed, an inactive coating film is formed on the surface of the positive electrode active material, thereby preventing the transfer of electrons and/or lithium ions. the

Also, the decomposed components generate highly active molecules in the electrolyte solution present in the pores of the electrode, thereby accelerating deterioration of the electrolyte solution or attacking (corroding) the positive electrode active material, thereby dissolving constituent elements of the positive electrode active material or reducing capacity. In order to suppress such a phenomenon, it is not sufficient to only stabilize the interface between the positive electrode active material particle and the electrolyte solution, and the above-mentioned stabilization and stabilization of the active molecules outside and near the positive electrode active material particle must be performed in a cooperative manner. the

In the lithium-containing transition metal oxide in the embodiment of the present invention, the metal element M2 other than the main transition metal inside the oxide particle is made to exist on the particle surface, so that the interface between the active material particle and the electrolytic solution is stabilized. In addition, making lithium-transition metal composite oxides containing at least one element selected from sulfur (S), phosphorus (P) and fluorine (F) exist in the vicinity of the particles in an aggregated form, so that active molecules are stabilized. It is believed that battery performance is greatly enhanced due to the synergistic effect of these stabilizing effects. the

Moreover, it is considered that the stabilizing effect of the metal element M2 is due to the fact that the metal element M2 is uniformly present in the inside of the particle in advance, and then the concentration of the metal element M2 at the particle surface is increased to ensure that the metal element M2 is uniformly present on the particle surface. Can be rendered at maximum, thus successfully improving battery performance. the

[Effect]

According to the nonaqueous electrolyte battery in the first embodiment of the present invention, deterioration of cycle characteristics can be suppressed, internal resistance rise due to charge-discharge cycles in a high-temperature environment can be suppressed, and thus increased capacity and improved battery characteristics. the

2. The second embodiment (second example of non-aqueous electrolyte battery)

A second embodiment of the present invention will be described. The nonaqueous electrolyte battery according to the second embodiment of the present invention uses a positive electrode active material having a more uniform coating. the

Since other materials and configurations are the same as in the first embodiment, explanations about them are omitted. the

[Positive electrode active material]

The positive electrode active material is, for example, composite oxide particles in which a metal element M2 different from the main transition metal M1 is contained and has a concentration gradient of the metal element M2 from the center of each particle toward the surface. The concentration gradient means that the concentration of the metal element M2 increases as the particle surface approaches. The composite oxide particle is a particle of a lithium-containing transition metal composite oxide in which at least one element X selected from sulfur (S), phosphorus (P) and fluorine (F) exists in an aggregated form on the surface of the composite oxide particle . the

In the second embodiment, the compound containing at least one element selected from sulfur (S), phosphorus (P) and fluorine (F) or a decomposition product of the compound has a melting point of 70°C or higher and 600°C or lower. The compound or the decomposition product of the compound positioned on the surface of the composite oxide by a certain means such as using a ball mill is melted by heating, thereby uniformly coating the surface of the composite oxide. Thereafter, the heated and molten compound or a decomposition product of the compound is reacted with the composite oxide. This results in a more efficient and uniform coating than that of the first embodiment. the

When the compound or the decomposition product of the compound is heated at a temperature higher than 600° C., a reaction in the composite oxide will be caused and the structure of the composite oxide may be changed. However, in the present embodiment, the compound or the decomposition product of the compound is melted and the composite oxide is coated to react with the composite oxide in a stable state before the structure of the composite oxide is changed. the

If the melting point of the compound or the decomposition product of the compound is higher than 600° C., the coating reaction starts before the compound or the product melts and coats the surface of the composite oxide particles, and the compound or the product and the composite oxide The reaction starts, which provides a partial coating reaction only at the sites where the compound or said product comes into contact with the complex oxide, which leads to an unfavorable non-uniform coating on the complex oxide. the

Heating at temperatures greater than 600° C. also leads to structural changes in the composite oxide. the

If the melting point of the compound or the decomposition product is less than 70° C., the compound or the product will unfavorably melt or decompose during deposition by a ball mill or the like. the

The compound or a decomposition product of the compound preferably has an average diameter of 30 μm or less. Such a diameter of the compound or the decomposition product will achieve a uniform coating of the complex oxide. When the diameter of the compound or the decomposition product is too large, they cannot be well mixed with the composite oxide using a ball mill or the like, which results in uneven deposition on the composite oxide. There is no lower limit to the diameter of the compound or the decomposition product. Smaller diameters will provide a more uniform coating. But the diameter is practically limited by the comminution of the compound or the decomposition product to about 1 μm. the

Examples of compounds are diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), ammonium sulfate ((NH ₄ ) ₂ HPO ₄ ), phosphoric acid (H ₃ PO ₄ ) wait. The cations of these compounds are removed by, for example, evaporation when heated, and thus a positive electrode active material free of impurities can be obtained, which can avoid reduction in capacity and other harmful effects.

As the metal element M2 different from the main transition metal M1, the same metal element M2 as in Embodiment Mode 1 can be employed. the

[Method for producing positive electrode active material] 

For example, the cathode active material of the second embodiment can be prepared according to the following procedure. the

First, the surfaces of the composite oxide particles are coated with a coating material. Regarding an exemplary method for coating the surface of the composite oxide particle, the same method as in the first embodiment can be employed, in which a lithium-transition metal containing the metal element M1 is pulverized by using a ball mill, a grinder, a pulverizer, or the like A composite oxide and a compound containing at least one element X selected from sulfur (S), phosphorus (P) and fluorine (F), are mixed and coated (deposited). the

In carrying out this operation, it is effective to add a certain amount of a liquid component, which may be water, for example. In addition, coating (deposition) by mechanochemical treatment or coating (deposition) with a metal compound by a vapor phase method such as sputtering, CVD (Chemical Vapor Deposition) or the like may also be employed. the

After allowing at least one element X selected from sulfur (S), phosphorus (P) and fluorine (F) to thereby exist on the lithium-transition metal composite oxide containing the metal element M1, heat treatment is preferably performed so that the metal element The concentration of M2 increases at the particle surface. For example, heat treatment may be performed at 700 to 900°C. The obtained lithium-transition metal composite oxide may be subjected to known techniques for controlling powder properties or some other use. the

During the heat treatment, the compound located on the surface of the composite oxide is melted into a liquid state and the surface of the composite oxide is uniformly coated with the compound. After further heat treatment, the compound is decomposed and the cations are removed, and the anions react with the metal element M2 included in the composite oxide. The temperature of the heat treatment may be raised after the compound is melted to react with the coating material. the

[Effect]

According to the second embodiment, the composite oxide may be coated with a coating material before the structure of the composite oxide is changed. Therefore, the function of the positive electrode active material can be improved, which leads to better performance of the nonaqueous electrolyte secondary battery. the

3. The third embodiment (the third example of the non-aqueous electrolyte battery)

A third embodiment of the present invention will be described. The nonaqueous electrolyte battery according to the third embodiment of the present invention uses an electrolytic solution instead of the gel electrolyte 16 in the nonaqueous electrolyte battery according to the first embodiment of the present invention. In this case, the electrolytic solution is used by impregnating the separator 15 therewith. As the electrolytic solution, the same electrolytic solution as that in the first embodiment can be used. the

For example, the nonaqueous electrolyte battery thus constructed can be manufactured in the following manner. First, the positive electrode 13 and the negative electrode 14 are fabricated. The positive electrode 13 and the negative electrode 14 can be manufactured in the same manner as in the first embodiment described above, so a detailed description of the manufacturing is omitted here. the

Next, after connecting the positive electrode lead 11 and the negative electrode lead 12 to the positive electrode 13 and the negative electrode 14, respectively, the positive electrode 13 and the negative electrode 14 are stacked together with the separator 15 in between to form a stack, the laminated body is wound, and the protective tape 17 is adhered to the outermost peripheral portion of the jellyroll. the

As a result, a wound electrode body having the same configuration as the wound electrode body 10 described above was obtained except that the electrolyte 16 was omitted. After the jelly roll is sandwiched between the packages 1 , an electrolytic solution is introduced into the inside of the packages 1 , and the packages 1 are sealed. In this way, the nonaqueous electrolyte battery according to the third embodiment of the present invention was obtained. the

[Effect]

According to the third embodiment of the present invention, the same effects as those of the first embodiment can be obtained. Specifically, deterioration of cycle characteristics can be suppressed, an increase in internal resistance due to charge-discharge cycles in a high-temperature environment can be suppressed, and thus increased capacity and improved battery characteristics can be simultaneously achieved. the

4. Fourth embodiment (fourth example of non-aqueous electrolyte battery)

Next, the configuration of a nonaqueous electrolyte battery according to a fourth embodiment of the present invention will be described with reference to FIGS. 3 and 4 . FIG. 3 shows the configuration of a nonaqueous electrolyte battery according to a fourth embodiment of the present invention. the

This nonaqueous electrolyte battery is a so-called cylindrical battery in which a wound strip-shaped positive electrode 31 and a strip-shaped negative electrode 32 are wound with a separator 33 therebetween to form a wound electrode body 30 which is provided in a substantially hollow The interior of the cylindrical battery case 21. the

The separator 33 is impregnated with an electrolytic solution as a liquid electrolyte. The battery case 21 is formed of, for example, iron (Fe) plated with nickel (Ni). The battery case 21 is closed at one end thereof and opened at the other end thereof. Inside the battery case 21 , a pair of insulating plates 22 and 23 are disposed on opposite sides of the wound electrode body 30 perpendicular to the outer peripheral surface of the wound electrode body 30 , respectively. the

At the open end of the battery case 21 , a battery cover 24 and a safety valve mechanism 25 and a PTC (Positive Temperature Coefficient) thermistor element 26 provided inside the battery cover 24 are mounted by caulking with a gasket 27 . Thereby, the inside of the battery case 21 is sealed. the

The battery cover 24 is made of, for example, the same material as the battery case 21 . The safety valve mechanism 25 is electrically connected to the battery cover 24 through the thermistor element 26 . The safety valve mechanism 25 is configured such that when the internal pressure of the battery exceeds a predetermined value due to an internal short circuit or external heating, the disc plate 25A is reversed to cut off electrical connection between the battery cover 24 and the wound electrode body 30 . the

When the temperature rises, the thermistor element 26 limits the current by increasing its resistance, thereby preventing abnormal heating caused by a large current. The gasket 27 is formed of, for example, an insulating material, and its surface is coated with asphalt. the

For example, the wound electrode body 30 is wound around the center pin 34 . In the wound electrode body 30 , a positive electrode lead 35 formed of aluminum (Al) or the like is connected to the positive electrode 31 , and a negative electrode lead 36 formed of nickel (Ni) or the like is connected to the negative electrode 32 . The positive electrode lead 35 is electrically connected to the battery cover 24 by welding to the safety valve mechanism 25 , and the negative electrode lead 36 is electrically connected to the battery can 21 by welding to the battery can 21 . the

FIG. 4 is a cross-sectional view showing a part of the wound electrical collective 30 shown in FIG. 3 in an enlarged manner. The wound electrical collective 30 has a structure in which a positive electrode 31 and a negative electrode 32 are stacked together with a separator 33 in between to form a stacked body, and the stacked body is wound. the

The positive electrode 31 includes, for example, a positive electrode current collector 31A and positive electrode active material layers 31B respectively provided on both sides of the positive electrode current collector 31A. The negative electrode 32 includes, for example, a negative electrode current collector 32A and negative electrode active material layers 32B respectively provided on both sides of the negative electrode current collector 31A. The positive electrode current collector 31A, the positive electrode active material layer 31B, the negative electrode current collector 32A, the negative electrode active material layer 32B, the diaphragm 33, and the electrolytic solution are respectively equivalent to the positive electrode current collector 13A, the positive electrode active material layer in the above-mentioned first battery. 13B, the negative electrode current collector 14A, the negative electrode active material layer 14B, the separator 15 and the electrolytic solution. the

[Method for producing non-aqueous electrolyte battery]

Now, a method of manufacturing the nonaqueous electrolyte battery according to the fourth embodiment of the present invention will be described below. The positive electrode 31 was manufactured as follows. First, a positive electrode active material and a binder are mixed with each other to prepare a positive electrode composition, which is dispersed in a solvent such as N-methyl-2-pyrrolidone to prepare a positive electrode composition slurry. Next, this positive electrode composition slurry was applied to the positive electrode current collector 31A, and dried. After that, compression molding is performed using a roll pressing machine or the like to form the positive electrode active material layer 31B, whereby the positive electrode 31 is obtained. the

The negative electrode 32 was produced in the following manner. First, a negative electrode active material and a binder are mixed with each other to prepare a negative electrode composition, which is dispersed in a solvent such as N-methyl-2-pyrrolidone to prepare a negative electrode composition slurry. Next, this negative electrode composition slurry was applied to the negative electrode current collector 32A, and the solvent was evaporated. After that, compression molding is performed using a roll press machine or the like to form the negative electrode active material layer 32B, whereby the negative electrode 32 is obtained. the

Subsequently, the positive electrode lead 35 is connected to the positive electrode current collector 31A by welding or the like, and the negative electrode lead 36 is connected to the negative electrode current collector 32A by welding or the like. Thereafter, the stack of positive electrode 31 and negative electrode 32 with separator 33 in between is wound, the top end of positive electrode lead 35 is welded to safety valve mechanism 25 , and the top end of negative electrode lead 36 is welded to battery case 21 . the

Then, the stacked body of the positive electrode 31 and the negative electrode 32 is sandwiched between the pair of insulating plates 22 and 23 , and housed in the battery case 21 . After the positive electrode 31 and the negative electrode 32 are accommodated in the battery can 21 , the electrolyte is introduced into the inside of the battery can 21 so that the separator 33 is impregnated with the electrolyte. the

After that, the battery cover 24 , the safety valve mechanism 25 and the thermistor element 26 are fixed to the open end of the battery case 21 by caulking with the gasket 27 . In this way, the nonaqueous electrolyte battery shown in Fig. 3 was manufactured. the

[Effect]

In the nonaqueous electrolyte battery according to the fourth embodiment of the present invention, gas generation can be suppressed, and battery rupture due to an increase in internal pressure can be prevented. the

5. Fifth embodiment (fifth example of non-aqueous electrolyte battery)

The nonaqueous electrolyte battery according to the fifth embodiment of the present invention uses a positive electrode active material having a more uniform coating instead of the positive electrode active material in the nonaqueous electrolyte battery of the fourth embodiment. the

Since other materials and configurations are the same as in the fourth embodiment, descriptions about them are omitted. the

[Positive electrode active material]

The mole fraction r(%) of the cathode active material of the fifth embodiment satisfies the formula 0.20≤r≤0.80 within the range that the ratio d(%) from the surface to a certain depth satisfies 0.020≤d≤0.050. The ratio d and the mole fraction r are determined according to the following formula. the

Ratio d (%)=[(mass of main transition metal M 1)+(mass of metal element M2)]/(mass of particle whole) (I)

Mole fraction r=(the amount of matter of the metal element M2)/[(the amount of matter of the main transition metal M1)+(the amount of matter of the metal element M2)] (II)

Except for the above points, the positive electrode active material of the fifth embodiment is the same as that of the fourth embodiment. the

The quality of the main transition metal M1 and the quality of the metal element M2 can be known as follows: the surface of the lithium-transition metal composite oxide is dissolved in a buffer solvent, and the mass content of the main transition metal M1 and metal element M2 dissolved in the buffer solvent is analyzed . the

Specifically, the ratio d (%) and the mole fraction ratio r can be determined as follows. First, a buffer solvent is added to the lithium-transition metal composite oxide particles and they are mixed. Then, the buffer solvent is sampled at regular intervals, and the solvent is filtered. The mass of the main transition metal M1 and the mass of the metal element M2 contained in each buffer solvent were measured by an inductively coupled plasma method. the

The amount [mol] of the metal M1 and the metal element M2 is calculated from the mass, and the ratio d and the mole fraction r are obtained according to formulas (I) and (II). Here, the particles are assumed to be spherical, and the calculation is performed under the assumption that the diameter of the particles dissolved in the buffer solvent becomes smaller while maintaining the spherical shape. the

The above analysis of the surface of the positive active material is three-dimensional and can provide quantitative analysis of the concentration gradient, which is difficult to achieve by conventional analysis methods of the surface state of the positive active material. the

Under the condition that the mole fraction ratio r(%) falls within the range of 0.20≤r≤0.80, where the ratio d(%) from the surface to a certain depth satisfies 0.020≤d≤0.050, the capacity retention rate and high-temperature storage capacity are relatively high. the

However, even if the mole fraction ratio r(%) falls within the range of 0.20≤r≤0.80, wherein the ratio d(%) from the surface to a certain depth does not satisfy 0.020≤d≤0.050, there is not necessarily capacity retention and Trend of improvement effect of high-temperature storage stability. the

Preferably, the ratio d (%) from the surface to a certain depth satisfies the range of 0.020≤d≤0.050, and the molar ratio r (%) decreases from the surface to the inside, because the reduction of capacity retention and high-temperature preservation can be avoided, especially A decrease in the capacity retention ratio can be significantly avoided. the

Except when the ratio d(%) from the surface to a certain depth satisfies 0.020≤d≤0.050, the mole fraction ratio r(%) falls within the range of 0.20≤r≤0.80, it is also preferred that the ratio d(%) from the surface to a certain depth ( %) satisfies 0.010≤d<0.020, and the molar ratio r satisfies 0.55≤r≤1.0, because reduction in discharge capacity can be avoided and cycle performance and high-temperature storage performance can be improved. the

[Method of manufacturing battery] 

A method of manufacturing the nonaqueous electrolyte secondary battery of the fifth embodiment is as follows. the

First, lithium-transition metal composite oxide particles containing lithium, a main transition metal M1, and a metal element M2 are mixed with a compound containing at least one element X selected from sulfur (S), phosphorus (P), and fluorine (F). mix. It is preferable to further mix a lithium-containing compound. Then, a compound containing at least one element X selected from sulfur (S), phosphorus (P) and fluorine (F) and preferably a compound containing lithium on the surface of the lithium-transition metal composite oxide is realized by mechanochemical treatment. deposition on. The mixture is mechanochemically treated for more than 5 minutes and less than 2 hours. When the mechanochemical treatment is shorter than 5 minutes, the coating is insufficient, and the positive electrode active material particles are pulverized into smaller particles having too small diameter. the

Next, the lithium-transition metal composite oxide particles were fired to obtain a positive electrode active material. The temperature for firing is preferably 500°C to 1500°C. If the temperature is lower than 500° C., the lithium-transition metal composite oxide particles cannot be sufficiently coated. However, if the temperature is higher than 1500° C., the particles aggregate into secondary particles, which leads to poor coatability on the collector. the

After firing, the lithium-transition metal composite oxide particles have a concentration gradient of the metal element M2 from the center toward the surface of each particle. The particles contain at least one element X selected from sulfur (S), phosphorus (P) and fluorine (F) deposited on the surface of the composite oxide particles in an aggregated form. the

Generally, the molar ratio r can be adjusted by using an added amount of a compound containing at least one element X selected from sulfur (S), phosphorus (P), and fluorine (F). When the compound is added too little, the reaction is too small to obtain a sufficient coating, and the molar ratio r decreases. When the added amount is larger, the molar ratio r becomes larger, but r will not be greater than 1 in principle. The reaction proceeds from the surface to the inside, so when the added amount is large, a high molar ratio is obtained from a portion where the ratio d (%) from the surface to a certain depth is large. the

When the coating material (ie, compound or decomposition product) and base material (ie, lithium-transition metal composite oxide) are not well mixed, the mole fraction ratio r decreases. For example, the compound has a diameter of 100 μm or more, which is larger than the average diameter of the positive electrode active material of 5 μm to 30 μm, and is non-uniformly dispersed. Therefore, a preferred coating state is not obtained, and the mole fraction ratio r sometimes becomes lower. Regarding the technique of mixing, any technique may be used as long as the substrate and the coating material are mixed well, such as a planetary mixer, a preliminary technique of shaking the mixture in a bag, and the like. the

After obtaining the positive electrode active material, the same procedure as in the fourth embodiment can be taken to obtain the nonaqueous electrolyte battery of the fifth embodiment. the

The upper limit of the charging voltage of the battery of the fourth embodiment may be 4.2V, but it is preferably designed to be higher than 4.2V. In particular, the battery is designed so that the upper limit of the charging voltage is preferably 4.25 V to 4.80 V, more preferably 4.35 V or more from the viewpoint of discharge capacity, and 4.65 V or less from the viewpoint of safety. The lower limit of the discharge voltage of the battery is preferably 2.00V to 3.30V. Designing high cell voltages results in high energy densities. the

6. Other implementation modes (deformation)

The present invention is not limited to the above-described embodiments of the present invention, and various modifications and applications are possible within the scope of the present invention. For example, the shape of the nonaqueous electrolyte battery is not limited to the above-mentioned type (cylindrical type), and may be, for example, a coin type. the

In addition, for example, a polymer solid electrolyte including an ion-conductive polymer material or an inorganic solid electrolyte including an ion-conductive inorganic material can be used as the electrolyte. Examples of ion-conductive polymer materials include polyethers, polyesters, polyphosphazenes, and polysiloxanes. Examples of inorganic solid electrolytes include ion-conducting ceramics, ion-conducting crystals, and ion-conducting glasses. the

The cathode active material of the fifth embodiment can be employed in the batteries of the first to third embodiments. the

[Example]

Now, the present invention will be specifically described by way of illustrated examples, which should not be construed as limiting the present invention. the

In Examples 1-1 to 1-13 and Comparative Examples 1-1 to 1-9, the addition volume of the coating material was changed, and the positive electrode materials having different distributions of the coating material on the surface of the composite oxide were determined. battery performance. the

<Example 1-1>

[Production of positive electrode]

Lithium carbonate (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ), aluminum hydroxide (Al(OH) ₃ ) and After magnesium carbonate (MgCO ₃ ), the mixture was fired at 900°C in air for 5 hours to obtain a lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ). The average particle diameter of the lithium-cobalt composite oxide measured by the laser light scattering method was 13 μm.

Subsequently, lithium carbonate (Li ₂ CO ₃ ) and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) were weighed and mixed with lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ), so as to obtain Co: Atomic ratio of Li:P=98:1:1. Then, the mixed material including lithium-cobalt composite oxide was treated by a mechanochemical system for 1 hour. As a result, a precursor before firing was obtained in which particles of lithium-cobalt composite oxide existed as a center material, and lithium carbonate and diammonium hydrogenphosphate were deposited on the surface of the particles.

The temperature of the precursor before firing was raised at a rate of 3°C/min and kept at 900°C for 3 hours, followed by slow cooling to obtain the lithium-transition metal composite oxide belonging to the present invention. The lithium-transition metal composite oxide has magnesium (Mg) uniformly distributed on the surface of lithium-cobalt composite oxide particles. In addition, the concentration of magnesium (Mg) is higher on the surface of the particle than inside the particle, and lithium phosphate (Li ₃ PO ₄ ) is dispersed on the particle surface.

Incidentally, the surface state of the lithium-transition metal composite oxide was confirmed by observing the obtained powder under SEM/EDX. After observing the surface of the lithium-transition metal composite oxide, uniform distribution of magnesium (Mg) on the particle surface and dispersion of phosphorus on the particle surface were confirmed. In addition, the magnesium concentration was confirmed by cutting the cross-section of the lithium-transition metal composite oxide and measuring the element distribution in the radial direction by Auger electron spectroscopy. After measuring the element distribution in the cross-section of the lithium-transition metal composite oxide, the concentration of magnesium was confirmed to continuously change from the surface to the inside of the particles. the

Furthermore, when the powder was subjected to measurement of a powder X-ray diffraction pattern by using CuKα, a diffraction peak corresponding to Li ₃ PO ₄ was confirmed in addition to a diffraction peak corresponding to LiCoO ₂ having a layered rock-salt structure.

By using the lithium-transition metal composite oxide obtained as above as a positive electrode active material, a nonaqueous electrolyte secondary battery was fabricated, and the high-temperature cycle characteristics and internal resistance change of the battery were evaluated as described below. the

A positive electrode composition was prepared by mixing 98 wt% of the above positive electrode active material, 0.8 wt% of amorphous carbon powder (Ketjen black), and 1.2 wt% of polyvinylidene fluoride (PVdF). The positive electrode composition was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode composition slurry, which was then uniformly applied to both sides of a positive electrode collector composed of strip-shaped aluminum foil. Subsequently, the positive electrode composition slurry on the surface of the positive electrode current collector was dried in a warm air current, and compression-molded using a roll pressing machine to form a positive electrode composition layer. the

[Manufacture of negative electrode]

The negative electrode composition was prepared by mixing 95 wt% graphite powder and 5 wt% PVdF. Disperse the negative electrode composition in N-methyl-2-pyrrolidone to prepare negative electrode composition slurry, which is then uniformly applied to both sides of the negative electrode collector made of strip-shaped copper foil, followed by heating Compression molding was carried out to form a negative electrode composition layer. the

[Preparation of electrolyte]

In a mixed solvent obtained by mixing ethylene carbonate (EC) and ethylmethyl carbonate (MEC) at a volume of 1:1, lithium hexafluorophosphate (LiPF ₆ ) was dissolved to obtain a concentration of 1 mol/dm ³ to prepare nonaqueous electrolyte.

[Assembly of battery]

The belt-shaped positive and negative electrodes produced as above were wound multiple times in a stacked state with the separator made of porous polyolefin in between to produce a spirally wound electrode body. The wound electrode body was housed in a battery case made of nickel-plated iron, and insulating plates were provided on and under the wound electrode body. Next, a negative electrode terminal made of nickel connected to the negative electrode current collector was welded to the bottom of the battery case. In addition, a positive electrode terminal made of aluminum connected to the positive electrode current collector was welded to the protrusion of the safety valve ensuring electrical conduction with the battery cover. the

Finally, the nonaqueous electrolytic solution was introduced into the battery case in which the wound electrode body had been incorporated. Afterwards, the battery case can be caulked by using an insulating sealing gasket to secure the valve, the PTC thermistor element, and the battery cover. In this way, a cylindrical battery having an outer diameter of 18 mm and a height of 65 mm was manufactured. the

[Evaluation of battery]

(a) Initial capacity

The cylindrical battery manufactured as above was subjected to constant current charging at a charging current of 1.5 A to a charging voltage of 4.35 V in an environment of an ambient temperature of 45°C. Then, the constant current charging was switched to the constant voltage charging, and the charging was ended when the total charging time reached 2.5 hours. Immediately thereafter, the battery was discharged with a discharge current of 2.0A, and the discharge was terminated when the battery voltage dropped to 3.0V. The discharge capacity in this case was measured as the initial capacity and found to be 9.1 Wh. the

(b) Capacity retention rate

The battery was subjected to repeated charge-discharge cycles under the same charge-discharge conditions as in the above case for measuring the initial capacity. After 300 cycles, the discharge capacity was measured, and the capacity retention rate based on the initial capacity was determined. The capacity retention rate was 82%. the

<Example 1-2>

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1 except that the battery voltage at the time of charging was 4.20V. When the battery was evaluated, it was found that the initial capacity was 8.0 Wh, and the capacity retention rate was 82%. Incidentally, the concentration distribution of elements in the positive electrode active material and the surface state of the particles of the active material in Examples 1-2 and the following Examples and Comparative Examples are shown in Table 1 below. the

<Example 1-3>

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1 except that the battery voltage at the time of charging was 4.4V. When the battery was evaluated, it was found that the initial capacity was 9.4 Wh, and the capacity retention rate was 80%. the

<Example 1-4>

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1 except that the battery voltage at the time of charging was 4.5V. When the battery was evaluated, it was found that the initial capacity was 10.0 Wh, and the capacity retention rate was 61%. the

<Example 1-5>

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that the coating material to be deposited on the lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ) was Ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ). When the battery was evaluated, it was found that the initial capacity was 9.1 Wh, and the capacity retention rate was 80%.

<Example 1-6>

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that the coating material to be deposited on the lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ) was Lithium hexafluorophosphate (LiPF ₆ ) and a firing temperature of 700°C. When the battery was evaluated, it was found that the initial capacity was 9.1 Wh, and the capacity retention rate was 81%.

<Example 1-7>

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that the coating material to be deposited on the lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ) was Lithium tetrafluoroborate (LiBF ₄ ) and the firing temperature is 700°C. When the battery was evaluated, it was found that the initial capacity was 9.1 Wh, and the capacity retention rate was 76%.

<Example 1-8>

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that the coating material to be deposited on the lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ) was Sulfur (S) and a firing temperature of 700°C. When the battery was evaluated, it was found that the initial capacity was 9.1 Wh, and the capacity retention rate was 64%.

<Example 1-9>

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ), lithium carbonate (Li ₂ CO ₃ ) and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ). When the battery was evaluated, it was found that the initial capacity was 9.1 Wh, and the capacity retention rate was 80%.

<Example 1-10>

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1-1, except that lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ), lithium carbonate (Li ₂ CO ₃ ) and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ). When the battery was evaluated, it was found that the initial capacity was 8.9 Wh, and the capacity retention rate was 75%.

<Example 1-11>

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1-1, except that lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ), lithium carbonate (Li ₂ CO ₃ ) and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ). When the battery was evaluated, it was found that the initial capacity was 8.2 Wh, and the capacity retention rate was 69%.

<Example 1-12>

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1-1 except that the composition of the lithium-cobalt composite oxide was LiCo _0.97 Al _0.01 Mg _0.02 O ₂ . When the battery was evaluated, it was found that the initial capacity was 9.0 Wh, and the capacity retention rate was 84%.

<Example 1-13>

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1-1 except that the composition of the lithium-cobalt composite oxide was LiCo _0.95 Al _0.01 Mg _0.04 O ₂ . When the battery was evaluated, it was found that the initial capacity was 8.8 Wh, and the capacity retention rate was 82%.

<Comparative example 1-1>

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1-1, except that the coating treatment of the lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ) was omitted. When the battery was evaluated, it was found that the initial capacity was 9.2 Wh, and the capacity retention rate was 31%.

<Comparative example 1-2>

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1-1, except that the coating treatment of the lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ) was omitted and the charging time The battery voltage is 4.2V. When the battery was evaluated, it was found that the initial capacity was 8.1 Wh, and the capacity retention rate was 71%.

<Comparative example 1-3>

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1-1, except that the coating treatment of the lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ) was omitted and the charging time The battery voltage is 4.4V. When the battery was evaluated, it was found that the initial capacity was 9.5 Wh, and the capacity retention rate was 25%.

<Comparative example 1-4>

A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that the composition of the lithium-cobalt composite oxide was LiCoO ₂ , to be deposited on the lithium-cobalt composite oxide (LiCoO ₂ ) The coating material on is a mixture of lithium carbonate (Li ₂ CO ₃ ), magnesium carbonate (MgCO ₃ ) and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), and the lithium-cobalt composite oxide ( LiCoO ₂ ), lithium carbonate (Li ₂ CO ₃ ), magnesium carbonate (MgCO ₃ ) and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), to obtain Co:Li:Mg:P=100:1:1:1 atomic ratio. When the battery was evaluated, it was found that the initial capacity was 9.1 Wh, and the capacity retention rate was 32%.

<Comparative example 1-5>

A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that the composition of the lithium-cobalt composite oxide was LiCoO ₂ , to be deposited on the lithium-cobalt composite oxide (LiCoO ₂ ) The coating material on is aluminum fluoride (AlF ₃ ), and lithium-cobalt composite oxide (LiCoO ₂ ) and aluminum fluoride (AlF ₃ ) are weighed and mixed to obtain an atomic ratio of Co:Al=100:1 . When the battery was evaluated, it was found that the initial capacity was 9.1 Wh, and the capacity retention rate was 30%.

<Comparative example 1-6>

A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that the composition of the lithium-cobalt composite oxide was LiCoO ₂ , to be deposited on the lithium-cobalt composite oxide (LiCoO ₂ ) The coating material on was aluminum phosphate (AlPO ₄ ), and lithium-cobalt composite oxide (LiCoO ₂ ) and aluminum phosphate (AlPO ₄ ) were weighed and mixed to obtain an atomic ratio of Co:Al=100:1. When the battery was evaluated, it was found that the initial capacity was 9.1 Wh, and the capacity retention rate was 25%.

<Comparative example 1-7>

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1-1, except that the composition of the lithium-cobalt composite oxide was LiCoO ₂ . When the battery was evaluated, it was found that the initial capacity was 9.1 Wh, and the capacity retention rate was 20%.

<Comparative example 1-8>

A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1-1, except that the composition of the lithium-cobalt composite oxide was LiCoO ₂ , to be deposited on the lithium-cobalt composite oxide (LiCoO ₂ ) The coating material on is lithium phosphate (Li ₃ PO ₄ ), and lithium-cobalt composite oxide (LiCoO ₂ ) and lithium phosphate (Li ₃ PO ₄ ) are weighed and mixed to obtain a Co:P=100:1 atomic ratio. When the battery was evaluated, it was found that the initial capacity was 9.1 Wh, and the capacity retention rate was 15%.

<Comparative example 1-9>

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1-1 except that after the treatment with diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) coating in the firing process The firing temperature is 300°C. When the battery was evaluated, it was found that the initial capacity was 8.6 Wh, and the capacity retention rate was 35%.

The evaluation results are shown in Table 1 below. the

As can be seen from the evaluation results, magnesium (Mg) is uniformly distributed from the inside to the surface of the composite oxide particles by using the positive electrode active material, and the surface of the particles is coated in such a way that sulfur (S), phosphorus ( P) and other examples can achieve capacity retention and good initial capacity. the

On the other hand, in Comparative Examples 1-1 to 1-3 in which no coating material was present, since the charging capacity of the battery was higher, the capacity retention rate was more significantly lowered. Furthermore, in Comparative Examples 1-4 to 1-6 in which the distribution of magnesium (Mg) within the oxide particles was not uniform, a high capacity retention ratio could not be maintained even if there was a concentration gradient. Also, in the absence of the above-mentioned metal element M2, even if sulfur (S), phosphorus (P) and the like are dispersed on the surface of the oxide particles, the capacity retention rate is low. the

In Examples 2-1 to 2-9, the coating material was changed and the battery performance of positive electrode materials having different coating materials on the surface of the composite oxide was obtained. the

<Example 2-1>

The same nonaqueous electrolyte secondary battery as in Example 1-1 was manufactured, and evaluated using a charge voltage of 4.35 V in the same manner as in Example 1-1, except that instead of lithium carbonate and hydrogen phosphate di Ammonium, diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) having an average diameter of 10 μm and a melting point of 190° C. as measured by laser light scattering was deposited on a lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ )superior. The initial capacity was 9.1 Wh and the capacity retention rate was 85%.

<Example 2-2>

The same nonaqueous electrolyte secondary battery as in Example 2-1 was produced except that ammonium sulfate ((NH ₄ ) ₂ HSO ₄ having an average diameter of 10 μm and a melting point of 513° C. ) deposited on lithium-cobalt composite oxide (LiCo _0.98 Al _0.0l Mg _0.01 O ₂ ). The initial capacity was 9.1 Wh and the capacity retention rate was 87%.

<Example 2-3>

The same nonaqueous electrolyte secondary battery as in Example 2-1 was produced except that diammonium hydrogen phosphate ((NH ₄ ) ₂ having an average diameter of 30 μm and a melting point of 190° C. HPO ₄ ) was deposited on lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ). The initial capacity was 9.1 Wh and the capacity retention rate was 80%.

<Example 2-4>

The same nonaqueous electrolyte secondary battery as in Example 2-1 was manufactured except that a lithium-cobalt composite oxide (LiNi _0.79 Co _0.19 Al _0.01 Mg _0.01 O ₂ ) was coated. The initial capacity was 10.9 Wh and the capacity retention rate was 81%.

<Example 2-5>

The same nonaqueous electrolyte secondary battery as in Example 2-1 was manufactured except that a lithium-cobalt composite oxide (LiNi _0.49 Co _0.19 Mn _0.29 Al _0.01 Mg _0.01 O ₂ ) was coated. The initial capacity was 9.5 Wh and the capacity retention rate was 80%.

<Example 2-6>

The same nonaqueous electrolyte secondary battery as in Example 2-1 was fabricated except that phosphoric acid (H ₃ PO ₄ ) having an average diameter of 10 μm and a melting point of 43° C. measured by a laser light scattering method was deposited on lithium - on cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ). The initial capacity was 9.1 Wh and the capacity retention rate was 53%.

<Example 2-7>

The same nonaqueous electrolyte secondary battery as in Example 2-1 was produced except that iron sulfate (Fe ₂ (SO ₄ ) ₃ having an average diameter of 10 μm and a melting point of 480° C. ) deposited on lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ). The initial capacity was 8.9 Wh and the capacity retention rate was 80%.

<Example 2-8>

The same nonaqueous electrolyte secondary battery as in Example 2-1 was produced except that diammonium hydrogen phosphate ((NH ₄ ) ₂ having an average diameter of 100 μm and a melting point of 190° C. HPO ₄ ) was deposited on lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ). The initial capacity was 9.1 Wh and the capacity retention rate was 58%.

<Example 2-9>

The same nonaqueous electrolyte secondary battery as in Example 2-1 was produced except that diammonium hydrogenphosphate ((NH ₄ ) ₂ having an average diameter of 100 μm and a melting point of 837° C. HPO ₄ ) was deposited on lithium-cobalt composite oxide (LiCo _0.98 Al _0.01 Mg _0.01 O ₂ ). The initial capacity was 9.0 Wh and the capacity retention rate was 60%.

The evaluation results are shown in Table 2 below. In Table 2, the results of Comparative Example 1-1 for reference are also shown. the

From the evaluation results, it can be seen that in Examples 2-1 to 2-5 in which the compound containing phosphorus P or fluorine F or the pyrolyzed compound has a melting point of 80° C. to 600° C., the capacity retention rate can be achieved. It can be assumed that when fired at 900° C., the compound containing phosphorus P or fluorine F or the pyrolyzed compound becomes liquid and uniformly coats the surface of the composite oxide. In these examples, the initial capacity remains high because the ammonium evaporates and is not retained in the active material. the

In embodiment 2-4 and 2-5, when using lithium-nickel-cobalt composite oxide or lithium-nickel-cobalt manganese composite oxide as the central material of positive active material, can obtain the concentration that makes metal element M2 A positive electrode active material with a concentration gradient increasing from the center of the composite oxide particle to the surface and good capacity retention. the

Regarding Examples 2-6, the capacity retention was improved, but the improvement due to coating was not very large. Because phosphoric acid dissolves and coats less effectively than those in Examples 2-1 to 2-5 during the mechanochemical treatment. This is because the melting point of phosphoric acid is lower than the temperature of mechanochemical treatment. the

Regarding Examples 2-7, since the melting point of the compound falls within the range of 70°C to 600°C, the coating is good, but the decomposed substance remains on the surface of the positive electrode, and since the impurity does not contribute to the charge or discharge reaction, the The initial discharge capacity is slightly lowered. the

In Examples 2-8, because the diameter of the coating material was too large, the coating material was not well mixed with the composite oxide. Therefore, the capacity retention ratio is improved, but the improvement due to coating is not so great. Because the melting point of the coating material is 837° C., which is higher than 600° C. and close to the firing temperature, which causes the coating material to react with the area of the complex oxide before the coating material melts and coats the complex oxide well, And destroys a good coating. the

In Examples 3-1 to 3-14 and Comparative Examples 3-1 to 3-14, the ratio d and the mole fraction ratio r were changed and battery characteristics were determined. the

In these examples, the ratio d and the mole fraction ratio r were obtained as follows. the

[ratio d and mole fraction ratio r]

A buffer solvent prepared with citric acid and sodium citrate to pH 5.1 was added to 0.2 g of lithium-transition metal composite oxide. The mixture was stirred and samples were filtered every minute with a 0.2 μm filter. The mass or volume concentration of the main transition metal M1 (i.e. Co) and the mass or volume concentration of the metal elements M2 (i.e. Mg, Mn, Ni) contained in each sample by ICP-AES: Inductively Coupled Plasma-Atomic Emission Spectrometry [HORIBAJY238ULTRACE] to obtain the mass of M1 and M2 dissolved in 10 mL of buffered solvent. Using this result, the amounts [mol] of M1 and M2 were calculated. The ratio d and the mole fraction ratio r are determined according to formulas (I) and (II). the

Ratio d (%)=[(mass of main transition metal M 1)+(mass of metal element M2)]/(mass of particle overall) (I)

Mole fraction r=(the amount of matter of the metal element M2)/[(the amount of matter of the main transition metal M1)+(the amount of matter of the metal element M2)] (II)

For capacity retention and high-temperature preservation, the coating including M2 is the most effective in which the ratio d satisfies 0.20≦r≦0.80, ie, from a surface of 10 nm to a depth of 100 nm. In the following examples, the mole fraction ratio r was varied with the ratio d in the range of 0.20≦r≦0.80 and the battery performance of each battery was examined. the

In the following examples, the distribution states of the metal element M2 and the element X are determined as follows. [Distribution state of metal element M2 and element X] 

Mg was examined by SEM/EDX to confirm whether Mg was uniformly distributed on the surface of the particles or whether P was scattered on the surface. The particles were dissected, and the elemental distribution along the diameter was measured by Auger electron spectroscopy to observe continuous changes in the Mg concentration. the

<Example 3-1>

The positive electrode active material was prepared as follows. the

The precursor for firing in the same manner as in Example 1-1 was heated up at a rate of 3°C/min and kept at 900°C for 3 hours, followed by slow cooling to obtain a lithium-transition metal composite oxide. The lithium-transition metal composite oxide has magnesium (Mg) uniformly distributed on the surface of lithium-cobalt composite oxide particles. In addition, the concentration of magnesium (Mg) is higher on the surface of the particle than inside the particle, and lithium phosphate (Li ₃ PO ₄ ) is dispersed on the particle surface.

In addition, the surface concentration gradient of magnesium Mg was confirmed in detail. The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.32, 0.30, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.46, 0.25, respectively. the

The surface state of the lithium-transition metal composite oxide was confirmed by observing the obtained powder under SEM/EDX. When observing the surface of the lithium-transition metal composite oxide, uniform distribution of magnesium (Mg) on the particle surface and dispersion of phosphorus on the particle surface were confirmed. By subjecting the powder to powder X-ray diffraction pattern measurement using CuKα, a diffraction peak corresponding to Li ₃ PO ₄ was confirmed in addition to a diffraction peak corresponding to LiCoO ₂ having a layered rock-salt structure. In addition, the magnesium concentration was confirmed by cutting the cross-section of the lithium-transition metal composite oxide and measuring the element distribution in the radial direction by Auger electron spectroscopy. After measuring the element distribution in the cross-section of the lithium-transition metal composite oxide, the concentration of magnesium was confirmed to continuously change from the surface to the inside of the particles.

A nonaqueous electrolyte secondary battery was manufactured according to the same method as in Example 1-1 by using the lithium-transition metal composite oxide obtained as above as a positive electrode active material. the

The initial capacity, capacity retention rate and high temperature storage performance of the battery were evaluated. The high-temperature storage performance was determined as follows. the

The battery manufactured as above was charged at a charging current of 1.5 A up to a charging voltage of 4.35 V in an environment of an ambient temperature of 45°C. Immediately thereafter, the battery was discharged with a discharge current of 2.0A, and the discharge was terminated when the battery voltage dropped to 3.0V. The battery was then subjected to high-temperature storage by remaining in an environment at an ambient temperature of 60° C. for 300 hours. After that, the discharge capacity after high-temperature storage was measured by discharging at 0.2C. Using the initial capacity and the discharge capacity after thermal storage, the high-temperature capacity retention rate, that is, the high-temperature storage property, was obtained according to the following equation. High temperature capacity retention [%]=(discharge capacity after heat preservation/initial capacity)×100. the

<Example 3-2>

In the same manner as in Example 3-1, a non-aqueous electrolyte secondary battery was prepared, and in the same manner as in Example 3-1, the evaluation of initial capacity, capacity retention rate and high-temperature storage retention performance was carried out, and the difference That is, the charging voltage is 4.2V. the

<Example 3-3>

In the same manner as in Example 3-1, a non-aqueous electrolyte secondary battery was prepared, and in the same manner as in Example 3-1, the evaluation of initial capacity, capacity retention rate and high-temperature storage retention performance was carried out, and the difference That is, the charging voltage is 4.5V. the

<Example 3-4>

A positive electrode active material was prepared in the same manner as in Example 3-1, except that the temperature of the second firing was set to 950° C., and the time of the second firing was 30 minutes. The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.22, 0.21, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.38, 0.16, respectively. In the same manner as in Example 3-1, a non-aqueous electrolyte secondary battery was prepared, and in the same manner as in Example 3-1, the evaluation of initial capacity, capacity retention rate and high-temperature storage retention performance was carried out, and the difference That is, the charging voltage is 4.5V. the

<Example 3-5>

A positive electrode active material was prepared in the same manner as in Example 3-1, except that the composite oxide as the base material was LiCo _0.95 Al _0.01 Mg _0.04 O ₂ . The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.73, 0.52, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.86, 0.44, respectively. A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage retention performance were performed in the same manner as in Example 3-1.

<Example 3-6>

A positive electrode active material was prepared in the same manner as in Example 3-1, except that the composite oxide as the base material was LiCo _0.97 Al _0.01 Mg _0.02 O ₂ . The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.31, 0.31, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.56, 0.25, respectively. A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage retention performance were performed in the same manner as in Example 3-1.

<Example 3-7>

Prepare the positive active material in the same manner as in Example 3-1, except that the composite oxide as the substrate is LiCoO ₃ and lithium carbonate Li ₂ CO ₃ , magnesium carbonate MgCO ₃ , ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ was mixed in the ratios shown in Table 3 and Table 4. The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.46, 0.40, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.55, 0.44, respectively. A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage retention performance were performed in the same manner as in Example 3-1.

<Example 3-8>

A positive electrode active material was prepared in the same manner as in Example 3-1, except that _LiCoO was used as the lithium-cobalt composite oxide for the substrate, and nickel hydroxide and manganese phosphate were used as coating materials coated. In the coating, the materials were prepared and mixed so that the mole fraction ratio r(Ni+Mn/Ni+Mn+Co) at the ratio d=0.02%, 0.05% was 0.35, 0.34, respectively, and at the ratio d=0.01%, The mole fraction ratios r at 0.10% were 0.56 and 0.25, respectively. A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage characteristics were performed in the same manner as in Example 3-1.

<Comparative example 3-1>

A composite oxide LiCo _0.98 Al _0.01 Mg _0.01 O ₂ without coating was used as the positive electrode active material. The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.01, 0.01, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.01, 0.01, respectively. A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage characteristics were performed in the same manner as in Example 3-1.

<Comparative example 3-2>

Prepare the positive electrode active material in the same manner as in Example 3-1, except that LiCoO ₂ is used as the lithium-cobalt composite oxide as the substrate, and Li ₂ CO ₃ with lithium carbonate, magnesium carbonate MgCO ₃ and ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ were mixed in a molar ratio of Co:Li:Mg:P=100:1:0.5:1. The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.18, 0.10, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.25, 0.08, respectively. A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage characteristics were performed in the same manner as in Example 3-1.

<Comparative example 3-3>

Prepare the positive electrode active material in the same manner as in Example 3-1, except that lithium-cobalt composite oxide LiCo _0.98 Al _0.01 Mg _0.01 O ₂ , lithium carbonate Li ₂ CO ₃ , magnesium carbonate MgCO ₃ and phosphoric acid Ammonium dihydrogen NH ₄ H ₂ PO ₄ was mixed in a molar ratio of Co:Li:Mg:P=100:1:1:4. The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.82, 0.83, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.80, 0.85, respectively. A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage characteristics were performed in the same manner as in Example 3-1.

<Comparative example 3-4>

A positive electrode active material was prepared in the same manner as in Example 3-1, except that the temperature of the second firing was set to 950° C., and the time of the second firing was 30 minutes. The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.22, 0.21, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.38, 0.16, respectively. A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage characteristics were performed in the same manner as in Example 3-1. the

<Comparative example 3-5>

A positive electrode active material was prepared in the same manner as in Example 3-1, except that LiCo _0.95 Al _0.01 Mg _0.04 O ₂ was used as a lithium-cobalt composite oxide as a base material. The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.73, 0.52, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.86, 0.44, respectively. A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage characteristics were performed in the same manner as in Example 3-1.

<Comparative example 3-6>

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Comparative Example 3-5. The initial capacity, capacity retention rate and high-temperature storage characteristics of the battery were evaluated in the same manner as in Example 3-1, except that the battery voltage at the time of charging was 4.2V. the

<Comparative example 3-7>

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Comparative Example 3-5. The initial capacity, capacity retention rate and high-temperature storage characteristics of the battery were evaluated in the same manner as in Example 3-1, except that the battery voltage at the time of charging was 4.5V. the

<Comparative example 3-8>

A positive electrode active material was prepared in the same manner as in Example 3-1, except that the second firing step was omitted. The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.80, 0.81, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.82, 0.79, respectively. A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage characteristics were performed in the same manner as in Example 3-1. the

<Comparative example 3-9>

A positive electrode active material was prepared in the same manner as in Example 3-1, except that mechanochemical treatment was performed for 15 minutes. The mole fraction ratios r at ratios d=0.02%, 0.05% were 0.21, 0.16, respectively. The mole fraction ratios r at ratios d=0.01%, 0.10% were 0.31, 0.14, respectively. A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage characteristics were performed in the same manner as in Example 3-1. the

<Comparative example 3-10>

A positive electrode active material was prepared in the same manner as in Example 3-1, except that _LiCoO was used as the lithium-cobalt composite oxide for the substrate, and was coated with a coating material of nickel hydroxide and manganese phosphate. cover. In the coating, materials are prepared and mixed so that the molar ratio of Ni:Co:Mn in the entire positive electrode active material particle=1:1:1, and the molar fraction ratio r at the ratio d=0.02%, 0.05% ( Ni+Mn/Ni+Mn+Co) were 0.25, 0.17, respectively, and the mole fraction ratios r at ratios d=0.01%, 0.10% were 0.30, 0.15, respectively. A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 3-1, and evaluations of initial capacity, capacity retention rate, and high-temperature storage characteristics were performed in the same manner as in Example 3-1.

The structures and evaluation results of the positive electrode active materials of the nonaqueous electrolyte secondary batteries of Examples 3-1 to 3-8 and Comparative Examples 3-1 to 3-10 are shown in Table 3 and Table 4 below. the

From the evaluation results, it can be seen that in Examples 3-1 to 3-8, good capacity retention and high-temperature storage characteristics can be achieved by controlling the decrease in initial capacity. On the other hand, in Comparative Examples 3-1 to 3-10, these effects were not obtained. the

The ratio d of the positive electrode active material of Examples 3-1 to 3-8 satisfies 0.02%≤d≤0.05%, and the mole fraction ratio r falls within the range of 0.20≤r≤0.80. And, they exhibit a tendency that the molar ratio r decreases from the surface to the depth direction in the range where the ratio d satisfies 0.02%≦d≦0.05%. the

When the ratio d (%) of a certain depth range (ie from the surface to 10nm to 100nm) satisfies 0.02%≤d≤0.05%, comparative examples 3-1 to 3-2, 3-4, 3-9 to 3-10 The mole fraction ratio r of the positive electrode active material is constant or decreases along the depth direction. But the mole fraction ratio r does not fall in the range of 0.20≤r≤0.80. the

The mole fraction ratio r of Comparative Example 3-1 was not in the range of 0.20≦r≦0.80 because no coating material was used. The mole fraction ratio r of Comparative Example 3-2 was not in the range of 0.20≦r≦0.80 because the mixing volume of the base material and the coating material was not appropriate. The mole fraction ratio r of Comparative Example 3-4 is not in the range of 0.20≦r≦0.80 because the second firing temperature is 750°C. The mole fraction ratio r of Comparative Example 3-9 is not in the range of 0.20≦r≦0.80 because the mechanochemical treatment time is 15 minutes, which is too short compared with Example 3-1. The mole fraction ratio r of Comparative Examples 3-10 was not in the range of 0.20≦r≦0.80 because the mixing volume of the base material and the coating material was not appropriate. the

When the ratio d(%) satisfies 0.02%≤d≤0.05%, the mole fraction ratio r of the cathode active material of Comparative Examples 3-3 and 3-8 falls outside the range of 0.20≤r≤0.80. And they show a tendency that the molar ratio r increases from the surface to the depth within a range in which the ratio d(%) satisfies 0.02%≦d≦0.05% in a certain depth range (ie, from 10nm to 100nm from the surface). the

The mole fraction ratio r of the cathode active material of Comparative Example 3-3 fell outside the range of 0.20≦r≦0.80 because the mixing volume of the base material and the coating material was not appropriate. The mole fraction ratio r of the positive electrode active material in Comparative Example 3-8 falls outside the range of 0.20≦r≦0.80 because the second firing treatment was not performed. the

The mole fraction ratio r of the cathode active materials of Comparative Examples 3-5 to 3-7 fell within the range of 0.20≦r≦0.80. But they show such a tendency: when the ratio d(%) satisfies 0.02%≤d≤0.05% in a certain depth range (i.e. from the surface to 10nm to 100nm), the mole fraction ratio r increases from the surface to the depth direction . the

The mole fraction ratio r of the positive electrode active material in Comparative Examples 3-5 to 3-7 increased because the temperature of the second firing treatment was 850°C. the

As shown above, when the ratio d satisfies 0.02%≤d≤0.05% in the range from the surface to a certain depth, and the mole fraction ratio r falls within the range of 0.20≤r≤0.80, by suppressing the initial capacity Dropping can achieve good capacity retention and high-temperature storage characteristics. the

Regarding the preparation method of the positive electrode active material, as in Examples 3-1 to 3-6, the metal element M2 is preferably introduced from the substrate to the surface. The preparation method makes the process simple, and the prepared material has a more uniform distribution at the surface and maintains the structure well, which improves the capacity retention rate and high-temperature storage characteristics. the

From the evaluation results in Table 4, it can be seen that the positive active material with a ratio d outside the range of 0.02%≤d≤0.05% does not necessarily improve the capacity retention and high-temperature storage characteristics, even if the mole fraction ratio r is in the range of 0.20≤r ≤0.80 range. the

As a method of analyzing the surface of the positive electrode active material, XPS (X-ray Photoelectron Spectroscopy) and TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) have been used so far. Table 3 shows the measured mole fraction ratio r, where the ratio d measured by these methods corresponding to the depth range along the depth direction is 0.010%, which corresponds to a region a few nm deep from the surface, and where the ratio d measured by the method The measured ratio d corresponding to the depth range in the depth direction is 0.100%, which corresponds to the region at a depth of more than 100 nm from the surface. the

<Example 3-9>

The non-aqueous electrolyte secondary battery manufactured as in Example 3-4 was disassembled, and the positive electrode current collector was peeled off from the electrode, the binder was removed from the positive electrode active material by immersion in NMP, and the conductive agent was burned to obtain Positive active material. The mole fraction ratios r at ratios d=0.02% and 0.05% were 0.29 and 0.22, respectively. the

<Example 3-10>

The nonaqueous electrolyte secondary battery manufactured as in Examples 3-5 was disassembled, and the positive electrode current collector was peeled off from the electrode, the binder was removed from the positive electrode active material by immersion in NMP, and the conductive agent was burned to obtain Positive active material. The mole fraction ratios r at ratios d=0.02% and 0.05% were 0.79 and 0.53, respectively. the

The structures and evaluation results of the positive electrode active materials of the nonaqueous electrolyte secondary batteries of Examples 3-9 and 3-10 are shown in Table 5 below. the

table 5

Notes:

u.: uniform, nu.: uneven, pr: exist, ab.: not exist, int.: scattered

Table 5 shows that when the positive electrode active material was removed from the nonaqueous electrolyte secondary battery, the mole fraction ratio r at the ratio d of 0.02% to 0.05% fell within the range of 0.20<r<0.80. the

<Example 3-11>

The positive electrode active material was prepared as follows. the

The same lithium-cobalt oxide LiCo _0.98 Al _0.01 Mg _0.01 O ₂ having an average diameter of 13 μm measured by the laser light scattering method as in Example 3-1 was mixed at an atomic ratio of Co:P=99:1 and passed through a jet mill Ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ comminuted to a mean diameter of 6 μm (measured by laser light scattering).

The mixture was treated by mechanochemical means for 1 hour to deposit ammonium dihydrogen phosphate on the surface of lithium-cobalt oxide to obtain a precursor before firing. The precursor was heated at a rate of 3°C/min and kept at 900°C for 3 hours, followed by slow cooling to obtain a lithium-transition metal composite oxide. The lithium-transition metal composite oxide has magnesium (Mg) uniformly distributed on the surface of the lithium-transition metal composite oxide particles. In addition, the concentration of magnesium (Mg) is higher on the particle surface than inside the particle, and lithium phosphate (Li ₃ PO ₄ ) is dispersed on the particle surface.

Incidentally, the surface concentration gradient of magnesium Mg was confirmed in detail. The mole fraction ratios r at ratios d=0.01%, 0.015%, 0.02%, 0.05% were 0.82, 0.73, 0.62, and 0.40, respectively. the

The surface state of the obtained material was confirmed by observing the obtained powder under SEM/EDX. Upon observation, uniform distribution of magnesium (Mg) on the particle surface and dispersion of phosphorus on the particle surface were confirmed. By measuring the powder X-ray diffraction pattern of the particles using CuKα, a diffraction peak corresponding to Li ₃ PO ₄ was confirmed in addition to a diffraction peak corresponding to LiCoO ₂ having a layered rock-salt structure. In addition, the magnesium concentration was confirmed by cutting the cross-section of the lithium-transition metal composite oxide and measuring the element distribution in the radial direction by Auger electron spectroscopy. When the element distribution in the cross-section of the particle was measured, the concentration of magnesium was confirmed to change continuously from the surface of the particle toward the inside.

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 3-1 by using the lithium-transition metal composite oxide particles obtained above as a positive electrode active material, and in the same manner as in Example 3-1 The initial capacity, capacity retention rate and high-temperature storage characteristics of the battery were evaluated. the

<Example 3-12>

A positive electrode active material was prepared in the same manner as in Example 3-11, except that lithium-cobalt oxide having an average diameter of 6 μm measured by a laser light scattering method was mixed at an atomic ratio of Co:P=98.8:1.2 LiCo _0.98 Al _0.01 Mg _0.01 O ₂ and ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ pulverized by a jet mill to an average diameter of 6 μm (measured by laser light scattering).

Incidentally, the surface concentration gradient of magnesium Mg was confirmed in detail. The mole fraction ratios r at ratios d=0.01%, 0.015%, 0.02%, 0.05% were 0.92, 0.85, 0.80, and 0.65, respectively. the

A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1-1 by using the lithium-transition metal composite oxide particles obtained as above as a positive electrode active material. And the batteries were evaluated for initial capacity, capacity retention rate and high-temperature storage characteristics in the same manner as in Example 3-11. the

<Example 3-13>

Lithium-cobalt oxides LiCo _0.98 Al _0.01 Mg _0.01 O ₂ with an average diameter of 6 μm (measured by laser light scattering) were mixed at an atomic ratio of Co:S=99:1 and pulverized by a jet mill into an average diameter of 3 μm (measured by laser light scattering). Ammonium sulfate (NH ₄ ) ₂ SO ₄ measured by scattering method. The mixture was processed through a planetary mixer for 30 minutes to deposit ammonium sulfate on the surface of the lithium-cobalt oxide. Except for the above process, a positive active material was prepared in the same manner as in Example 3-11. The mole fraction ratios r at ratios d=0.01%, 0.015%, 0.02%, 0.05% were 0.80, 0.71, 0.58, and 0.38, respectively.

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 3-11 by using the lithium-transition metal composite oxide particles obtained above as a positive electrode active material. And the batteries were evaluated for initial capacity, capacity retention rate and high-temperature storage characteristics in the same manner as in Example 3-11. the

<Example 3-14>

The positive electrode active material was prepared in the same manner as in Example 3-11, except that ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ was mixed at an atomic ratio of Co:P=99:1 and had a laser light scattering method. Measured 100 μm average diameter lithium cobalt oxide.

Incidentally, the surface concentration gradient of magnesium Mg was confirmed in detail. The mole fraction ratios r at ratios d=0.01%, 0.015%, 0.02%, 0.05% were 0.62, 0.53, 0.44, and 0.25, respectively. the

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 3-11 by using the lithium-transition metal composite oxide particles obtained above as a positive electrode active material. And the batteries were evaluated for initial capacity, capacity retention rate and high-temperature storage characteristics in the same manner as in Example 3-11. the

<Comparative example 3-11>

The positive electrode active material was prepared in the same manner as in Example 3-11, except that ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ was mixed at an atomic ratio of Co:P=95:5 and was obtained by the laser light scattering method. Measured 6 μm average diameter lithium cobalt oxide.

Incidentally, the surface concentration gradient of magnesium Mg was confirmed in detail. The mole fraction ratios r at ratios d=0.01%, 0.015%, 0.02%, 0.05% were 0.98, 0.95, 0.92, and 0.85, respectively. the

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 3-11 by using the lithium-transition metal composite oxide particles obtained above as a positive electrode active material. And the batteries were evaluated for initial capacity, capacity retention rate and high-temperature storage characteristics in the same manner as in Example 3-11. the

<Comparative example 3-12>

A positive electrode active material was prepared in the same manner as in Example 3-11, except that ammonium sulfate (NH ₄ ) ₂ SO ₄ was mixed at an atomic ratio of Co:S=99:1 and had a value measured by a laser light scattering method. LiCoO with an average diameter of 6 μm.

Incidentally, the surface concentration gradient of magnesium Mg was confirmed in detail. The mole fraction ratios r at ratios d=0.01%, 0.015%, 0.02%, 0.05% were 0.33, 0.25, 0.20, and 0.15, respectively. the

A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 3-11 by using the lithium-transition metal composite oxide particles obtained above as a positive electrode active material. And the batteries were evaluated for initial capacity, capacity retention rate and high-temperature storage characteristics in the same manner as in Example 3-11. the

The structures and evaluation results of the positive electrode active materials of the nonaqueous electrolyte secondary batteries of Examples 3-11 to 3-14 and Comparative Examples 3-11 to 3-12 are shown in Table 6 below. the

As can be seen from the evaluation results shown in Table 6, in the range where the ratio d satisfies 0.02%≤d≤0.05%, the mole fraction ratio r of the positive electrode active material of Examples 3-11, 3-12, and 3-13 falls In the range 0.20≤r≤0.80. And at the same time, in the range where the ratio d satisfies 0.01%≤d<0.02%, the mole fraction ratio r falls within the range 0.55≤r<1.0. These Examples exhibit greatly improved retention capacity ratios and high-temperature storage characteristics by suppressing a decrease in their discharge capacity. the

In the range where the ratio d satisfies 0.02%≤d≤0.05%, the mole fraction ratio r of the positive active material of Examples 3-14 falls within the range 0.20≤r≤0.80. But in the range where the ratio d satisfies 0.01%≤d<0.02%, the mole fraction ratio r does not fall within the range 0.55≤r<1.0. Examples 3-14 could not obtain highly improved retention capacity or high-temperature storage properties. Since the average diameter of the coating material ammonium dihydrogen phosphate is 100 μm, this disturbs the fine mixing state of the ammonium dihydrogen phosphate, so that a good coating state cannot be obtained on the surface of the substrate. the

In the range where the ratio d satisfies 0.01%≤d<0.02%, the mole fraction ratio r of the positive electrode active material of Comparative Example 3-11 falls within the range 0.55≤r<1.0. But in the range where the ratio d satisfies 0.02%≤d≤0.05%, the mole fraction ratio r falls outside the range 0.20≤r≤0.80. This is because too much coating material makes the coating too thick, which reduces positive electrode active material that contributes to charge-discharge capacity. Therefore, the initial discharge capacity of Comparative Examples 3-11 was small. the

In the range where the ratio d satisfies 0.01%≤d<0.02%, the mole fraction ratio r of the positive electrode active material in Comparative Example 3-12 falls outside the range of 0.55≤r<1.0. This is because the coating material does not mix well with the substrate and does not give a good coating. Therefore, good improvements in retention capacity and high-temperature storage characteristics could not be obtained by Comparative Examples 3-12. the

It should be understood by those skilled in the art that various alterations, combinations, sub-combinations and changes may be made depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof. the

Claims (18)

1. A positive electrode active material, prepared by the following steps: mixing a lithium-containing compound, a compound containing a transition metal to be contained in a solid solution, and a compound containing a metal element M2 other than the transition metal, and firing the mixture to form composite oxide particles; depositing a compound containing at least one element selected from sulfur S, phosphorus P, and fluorine F on the surface of the composite oxide particle; and firing said composite oxide particles on which a compound containing at least one element selected from sulfur S, phosphorus P and fluorine F is deposited; Each of the composite oxide particles thus has a concentration gradient such that the concentration of the metal element M2 increases from the center toward the surface of the composite oxide particle, and At least one element selected from the group consisting of sulfur S, phosphorus P, and fluorine F is allowed to exist in a form accumulated on the surface of the composite oxide particles. 2. the positive electrode active material according to claim 1, Wherein, the transition metal is at least one selected from nickel Ni, cobalt Co, manganese Mn and iron Fe. 3. positive electrode active material according to claim 1, Wherein, the metal element M2 is at least one selected from manganese Mn, magnesium Mg, aluminum Al, nickel Ni, boron B, titanium Ti, cobalt Co and iron Fe. 4. positive electrode active material according to claim 1, Here, the composite oxide particles on which a compound containing at least one element selected from sulfur S, phosphorus P, and fluorine F is deposited are fired in the presence of a lithium-containing compound. 5. positive electrode active material according to claim 1, wherein, The compound containing at least one element selected from sulfur S, phosphorus P, and fluorine F or a thermal decomposition product of the compound has a melting point of 70°C or higher and 600°C or lower. 6. positive electrode active material according to claim 1, wherein, The compound containing at least one element selected from sulfur S, phosphorus P, and fluorine F or a thermal decomposition product of the compound has an average diameter of 30 μm or less. 7. A positive electrode active material comprising a lithium-transition metal composite oxide, the lithium-transition metal composite oxide comprising lithium, a main transition metal M1 and a metal element M2 different from the main transition metal M1, wherein, The metal element M2 has a concentration gradient of the metal element M2 from the center to the surface of each particle, In the range of the ratio d(%) from the surface to a certain depth satisfying 0.020≤d≤0.050, the mole fraction r(%) satisfies the formula 0.20≤r≤0.80, Wherein, the ratio d(%)=[(the mass of the main transition metal M1)+(the mass of the metal element M2)]/(the mass of the whole particle), and Mole fraction r=(substance amount of metal element M2)/[(substance amount of main transition metal M1)+(substance amount of metal element M2)]. 8. positive electrode active material according to claim 7, wherein, In the range where the ratio d(%) from the surface to a certain depth satisfies 0.010≤d<0.020, the mole fraction r(%) satisfies the formula 0.55≤r<1.00. 9. positive electrode active material according to claim 7, wherein, The mole fraction ratio r decreases from the surface of the composite oxide particle toward the center within a range in which the ratio d (%) from the surface to the depth satisfies 0.020≦d≦0.050. 10. positive electrode active material according to claim 8, wherein, In the range where the ratio d (%) from the surface to the depth satisfies 0.010≦d<0.020, the mole fraction ratio r decreases from the surface of the composite oxide particle toward the center. 11. positive electrode active material according to claim 8, wherein, At least one element X selected from sulfur S, phosphorus P, and fluorine F exists on the surface in an aggregated form. 12. positive electrode active material according to claim 11, wherein, By the reaction between the lithium-transition metal composite oxide particles and the compound including at least one element selected from sulfur S, phosphorus P, and fluorine F, the concentration of the metal element M2 at the surface Increase. 13. positive electrode active material according to claim 12, wherein, A compound comprising lithium is simultaneously present during the reaction. 14. A positive electrode, comprising a positive electrode active material prepared by the following steps: mixing a lithium-containing compound, a compound containing a transition metal to be contained in a solid solution, and a compound containing a metal element M2 other than the transition metal, and firing the mixture to form composite oxide particles; depositing a compound containing at least one element selected from sulfur S, phosphorus P, and fluorine F on the surface of the composite oxide particle; and firing said composite oxide particles on which a compound containing at least one element selected from sulfur S, phosphorus P and fluorine F is deposited; Each of the composite oxide particles thus has a concentration gradient such that the concentration of the metal element M2 increases from the center toward the surface of the composite oxide particle, and At least one element selected from the group consisting of sulfur S, phosphorus P, and fluorine F is allowed to exist in a form accumulated on the surface of the composite oxide particles. 15. A nonaqueous electrolyte battery comprising a positive pole, a negative pole and an electrolyte: Wherein, the positive electrode includes a positive electrode active material prepared by the following steps: mixing a lithium-containing compound, a compound containing a transition metal to be contained in a solid solution, and a compound containing a metal element M2 other than the transition metal, and firing the mixture to form composite oxide particles; depositing a compound containing at least one element selected from sulfur S, phosphorus P, and fluorine F on the surface of the composite oxide particle; and firing said composite oxide particles on which a compound containing at least one element selected from sulfur S, phosphorus P and fluorine F is deposited; Each of the composite oxide particles thus has a concentration gradient such that the concentration of the metal element M2 increases from the center toward the surface of the composite oxide particle, and It exists in a form in which at least one element selected from sulfur S, phosphorus P, and fluorine F is accumulated on the surface of the composite oxide particles. 16. A method for preparing a positive electrode active material, comprising the following steps: mixing a lithium-containing compound, a compound containing a transition metal to be contained in a solid solution, and a compound containing a metal element M2 other than the transition metal, and firing the mixture to form composite oxide particles; depositing a compound containing at least one element selected from sulfur S, phosphorus P, and fluorine F on the surface of the composite oxide particle; and firing said composite oxide particles on which a compound containing at least one element selected from sulfur S, phosphorus P and fluorine F is deposited; Each of the composite oxide particles thus has a concentration gradient such that the concentration of the metal element M2 increases from the center toward the surface of the composite oxide particle, and At least one element selected from the group consisting of sulfur S, phosphorus P, and fluorine F is allowed to exist in a form accumulated on the surface of the composite oxide particles. 17. The method for preparing positive electrode active material according to claim 16, wherein, In the firing process, the compound containing at least one element selected from sulfur S, phosphorus P, and fluorine F is melted or thermally decomposed and then melted, and the molten compound is uniformly coated on the composite oxide particles s surface. 18. the method for preparing positive electrode active material according to claim 17, wherein, During the firing process, the cations from the deposition compound containing at least one element selected from sulfur S, phosphorus P and fluorine F are removed, and the cations from the deposition compound containing at least one element selected from sulfur S, phosphorus P and fluorine F are removed. Anions of the deposition compound react with elements included in the composite oxide particles.

Images